I wouldn't say it is deprecated, just not supported in graphics mode yet.
Here's all the sprite constants that are declared; use them. (Spoilered for length)
core.declare( "SPRITE_PLAYER", OBJECT_ROW_1 + 1 )
core.declare( "SPRITE_PLAYER_KNIFE", OBJECT_ROW_1 + 2 )
core.declare( "SPRITE_PLAYER_CHAINSAW", OBJECT_ROW_1 + 3 )
core.declare( "SPRITE_PLAYER_PISTOL", OBJECT_ROW_1 + 4 )
core.declare( "SPRITE_PLAYER_SHOTGUN", OBJECT_ROW_1 + 5 )
core.declare( "SPRITE_PLAYER_CSHOTGUN", OBJECT_ROW_1 + 6 )
core.declare( "SPRITE_PLAYER_DSHOTGUN", OBJECT_ROW_1 + 7 )
core.declare( "SPRITE_PLAYER_CHAINGUN", OBJECT_ROW_1 + 8 )
core.declare( "SPRITE_PLAYER_BAZOOKA", OBJECT_ROW_1 + 9 )
core.declare( "SPRITE_PLAYER_PLASMA", OBJECT_ROW_1 + 10 )
core.declare( "SPRITE_PLAYER_BFG9000", OBJECT_ROW_1 + 11 )
core.declare( "SPRITE_PLAYER_SPEAR", OBJECT_ROW_1 + 12 )
--
core.declare( "SPRITE_PLAYER_STAFF", OBJECT_ROW_1 + 14 )
core.declare( "SPRITE_PLAYER_CLEAVER", OBJECT_ROW_1 + 15 )
core.declare( "SPRITE_PLAYER_DRAGON", OBJECT_ROW_1 + 16 )
--
core.declare( "SPRITE_KNIFE", OBJECT_ROW_2 + 2 )
core.declare( "SPRITE_CHAINSAW", OBJECT_ROW_2 + 3 )
core.declare( "SPRITE_PISTOL", OBJECT_ROW_2 + 4 )
core.declare( "SPRITE_SHOTGUN", OBJECT_ROW_2 + 5 )
core.declare( "SPRITE_CSHOTGUN", OBJECT_ROW_2 + 6 )
core.declare( "SPRITE_DSHOTGUN", OBJECT_ROW_2 + 7 )
core.declare( "SPRITE_CHAINGUN", OBJECT_ROW_2 + 8 )
core.declare( "SPRITE_BAZOOKA", OBJECT_ROW_2 + 9 )
core.declare( "SPRITE_PLASMA", OBJECT_ROW_2 + 10 )
core.declare( "SPRITE_BFG9000", OBJECT_ROW_2 + 11 )
core.declare( "SPRITE_SPEAR", OBJECT_ROW_2 + 12 )
core.declare( "SPRITE_BFG10K", OBJECT_ROW_2 + 13 )
core.declare( "SPRITE_STAFF", OBJECT_ROW_2 + 14 )
core.declare( "SPRITE_CLEAVER", OBJECT_ROW_2 + 15 )
core.declare( "SPRITE_DRAGON", OBJECT_ROW_2 + 16 )
core.declare( "SPRITE_ARMOR", OBJECT_ROW_3 + 1 )
core.declare( "SPRITE_AARMOR", OBJECT_ROW_3 + 2 )
core.declare( "SPRITE_SBOOTS", OBJECT_ROW_3 + 3 )
core.declare( "SPRITE_BOOTS", OBJECT_ROW_3 + 4 )
core.declare( "SPRITE_MOD", OBJECT_ROW_3 + 5 )
core.declare( "SPRITE_SKULL", OBJECT_ROW_3 + 6 )
core.declare( "SPRITE_AMMO", OBJECT_ROW_3 + 7 )
core.declare( "SPRITE_PAMMO", OBJECT_ROW_3 + 8 )
core.declare( "SPRITE_SHELL", OBJECT_ROW_3 + 9 )
core.declare( "SPRITE_PSHELL", OBJECT_ROW_3 + 10 )
core.declare( "SPRITE_ROCKET", OBJECT_ROW_3 + 11 )
core.declare( "SPRITE_PROCKET", OBJECT_ROW_3 + 12 )
core.declare( "SPRITE_CELL", OBJECT_ROW_3 + 13 )
core.declare( "SPRITE_PCELL", OBJECT_ROW_3 + 14 )
core.declare( "SPRITE_PHASE", OBJECT_ROW_3 + 15 )
--
core.declare( "SPRITE_BACKPACK", OBJECT_ROW_4 + 1 )
core.declare( "SPRITE_ENVIRO", OBJECT_ROW_4 + 2 )
core.declare( "SPRITE_HGLOBE", OBJECT_ROW_4 + 3 )
core.declare( "SPRITE_LHGLOBE", OBJECT_ROW_4 + 4 )
core.declare( "SPRITE_SUPERCHARGE",OBJECT_ROW_4 + 5 )
core.declare( "SPRITE_INV", OBJECT_ROW_4 + 6 )
core.declare( "SPRITE_MEGASPHERE", OBJECT_ROW_4 + 7 )
core.declare( "SPRITE_SHARD", OBJECT_ROW_4 + 8 )
core.declare( "SPRITE_MEDPACK", OBJECT_ROW_4 + 9 )
core.declare( "SPRITE_LMEDPACK", OBJECT_ROW_4 + 10 )
core.declare( "SPRITE_BERSERK", OBJECT_ROW_4 + 11 )
core.declare( "SPRITE_MAP", OBJECT_ROW_4 + 12 )
core.declare( "SPRITE_TMAP", OBJECT_ROW_4 + 13 )
core.declare( "SPRITE_SCHEMATIC", OBJECT_ROW_4 + 14 )
core.declare( "SPRITE_LIGHTAMP", OBJECT_ROW_4 + 15 )
core.declare( "SPRITE_NUKE", OBJECT_ROW_4 + 16 )
core.declare( "SPRITE_FORMER", OBJECT_ROW_5 + 1 )
core.declare( "SPRITE_SERGEANT", OBJECT_ROW_5 + 2 )
core.declare( "SPRITE_CAPTAIN", OBJECT_ROW_5 + 3 )
core.declare( "SPRITE_COMMANDO", OBJECT_ROW_5 + 4 )
core.declare( "SPRITE_IMP", OBJECT_ROW_5 + 5 )
core.declare( "SPRITE_DEMON", OBJECT_ROW_5 + 6 )
core.declare( "SPRITE_LOSTSOUL", OBJECT_ROW_5 + 7 )
core.declare( "SPRITE_CACODEMON", OBJECT_ROW_5 + 8 )
core.declare( "SPRITE_PAIN", OBJECT_ROW_5 + 9 )
core.declare( "SPRITE_KNIGHT", OBJECT_ROW_5 + 10 )
core.declare( "SPRITE_BARON", OBJECT_ROW_5 + 11 )
core.declare( "SPRITE_ARACHNO", OBJECT_ROW_5 + 12 )
core.declare( "SPRITE_ARCHVILE", OBJECT_ROW_5 + 13 )
core.declare( "SPRITE_REVENANT", OBJECT_ROW_5 + 14 )
core.declare( "SPRITE_MANCUBUS", OBJECT_ROW_5 + 15 )
core.declare( "SPRITE_BRUISER", OBJECT_ROW_5 + 16 )
core.declare( "SPRITE_AGONY", OBJECT_ROW_6 + 9 )
core.declare( "SPRITE_MASTER", OBJECT_ROW_7 + 1 )
core.declare( "SPRITE_LAVAELEM", OBJECT_ROW_7 + 2 )
core.declare( "SPRITE_ANGEL", OBJECT_ROW_7 + 3 )
core.declare( "SPRITE_SHAMBLER", OBJECT_ROW_7 + 4 )
core.declare( "SPRITE_JC", OBJECT_ROW_7 + 5 )
core.declare( "SPRITE_CYBERDEMON",OBJECT_ROW_7 + 6 )
core.declare( "SPRITE_MASTERMIND",OBJECT_ROW_7 + 10 )
core.declare( "SPRITE_LAVAINV" ,OBJECT_ROW_8 + 2 )
core.declare( "SPRITE_DOOR", OBJECT_ROW_14 + 1 )
core.declare( "SPRITE_OPENDOOR", OBJECT_ROW_14 + 2 )
core.declare( "SPRITE_HELLDOOR", OBJECT_ROW_14 + 3 )
core.declare( "SPRITE_HELLOPENDOOR", OBJECT_ROW_14 + 4 )
core.declare( "SPRITE_BARREL", OBJECT_ROW_14 + 5 )
core.declare( "SPRITE_LAVABARREL", OBJECT_ROW_14 + 6 )
core.declare( "SPRITE_ACIDBARREL", OBJECT_ROW_14 + 7 )
--
--
core.declare( "SPRITE_TREE", OBJECT_ROW_14 + 10 )
core.declare( "SPRITE_SHOT", OBJECT_ROW_15 + 1 )
core.declare( "SPRITE_CSHOT", OBJECT_ROW_15 + 2 )
core.declare( "SPRITE_BLAST", OBJECT_ROW_15 + 3 )
core.declare( "SPRITE_ROCKETSHOT", OBJECT_ROW_15 + 4 )
core.declare( "SPRITE_GRAYSTAIRS", OBJECT_ROW_15 + 5 )
core.declare( "SPRITE_EXPLOSION", OBJECT_ROW_15 + 6 )
core.declare( "SPRITE_PLASMASHOT", OBJECT_ROW_15 + 7 )
core.declare( "SPRITE_BFGSHOT", OBJECT_ROW_15 + 8 )
core.declare( "SPRITE_FIREBALL", OBJECT_ROW_15 + 9 )
core.declare( "SPRITE_PLASMABALL", OBJECT_ROW_15 + 10 )
core.declare( "SPRITE_ACIDSHOT", OBJECT_ROW_15 + 11 )
--
core.declare( "SPRITE_ARROW", OBJECT_ROW_16 + 1 )
core.declare( "SPRITE_SELECT", OBJECT_ROW_16 + 2 )
core.declare( "SPRITE_MARK", OBJECT_ROW_16 + 3 )
core.declare( "SPRITE_STAIRS", OBJECT_ROW_16 + 4 )
core.declare( "SPRITE_REDSTAIRS", OBJECT_ROW_16 + 5 )
core.declare( "SPRITE_PORTAL", OBJECT_ROW_16 + 6 )
core.declare( "SPRITE_TELEPORT", OBJECT_ROW_16 + 7 )
core.declare( "SPRITE_LEVER", OBJECT_ROW_16 + 8 )
core.declare( "SPRITE_BLOOD", OBJECT_ROW_16 + 9 )
core.declare( "SPRITE_BLOODPOOL", OBJECT_ROW_16 + 10 )
core.declare( "SPRITE_CORPSE", OBJECT_ROW_16 + 11 )
core.declare( "SPRITE_WALLBLOOD", OBJECT_ROW_16 + 12 )
core.declare( "SPRITE_GRID", OBJECT_ROW_16 + 13 )
--
core.declare( "SPRITE_FLOOR", TERRAIN_ROW_1 + 1 )
core.declare( "SPRITE_CAVEFLOOR", TERRAIN_ROW_2 + 1 )
core.declare( "SPRITE_HELLFLOOR", TERRAIN_ROW_3 + 1 )
core.declare( "SPRITE_WALL", TERRAIN_ROW_10 + 1 )
core.declare( "SPRITE_CAVEWALL", TERRAIN_ROW_10 + 4 )
core.declare( "SPRITE_BRICKWALL", TERRAIN_ROW_10 + 7 )
core.declare( "SPRITE_TECHWALL", TERRAIN_ROW_10 + 10 )
core.declare( "SPRITE_BOSSWALL", TERRAIN_ROW_10 + 13 )
core.declare( "SPRITE_WATER", TERRAIN_ROW_15 + 1 )
core.declare( "SPRITE_ACID", TERRAIN_ROW_15 + 3 )
core.declare( "SPRITE_LAVA", TERRAIN_ROW_15 + 5 )
core.declare( "SPRITE_BRIDGE", TERRAIN_ROW_15 + 7 )
core.declare( "SPRITE_YBOX", TERRAIN_ROW_15 + 8 )
core.declare( "SPRITE_WBOX", TERRAIN_ROW_15 + 9 )
core.declare( "SPRITE_YBOXC", TERRAIN_ROW_16 + 8 )
core.declare( "SPRITE_WBOXC", TERRAIN_ROW_16 + 9 )
Alternatively, you could also just copy the values from things you know like beings.imp.sprite.
The value needs to be the number id of the missile. Number ids are subject to change between versions, so you should translate from the string id e.g.
Honestly, I suspect there are still bugs in power_backpack ;) But no, I'm not aware of any other code that resorts the inventory like this; it is tied together with the backpack flag.