Do assemblies still count has having x amount of mod slots taken up, or can you proceed to throw more on there?
I'm wondering because my Tactical Armor won't let me throw a power mod on it, and I'm not sure if it's specifically blocked out from further mods or if its mod slots are all considered used up.
Under normal circumstances, assemblies are unmoddable. This is essentially a way to properly balance them, since a lot of assemblies are similar to exotics: while you are allowed to "create exotics", you are limited in the modding department, so in many cases, the assembled counterparts are equal to unmodded exotics, the latter of which can surpass the former once mods are gained.
However, by investing in Whizkid(2) BEFORE assembling a piece of equipment, you can add a single mod on top of it. So yes, if you wait long enough, you can make a power-modded tactical armor. It's a tough decision to hold on to your mods for a while longer, but it can often be worth it in the long run. (Note that you do not need to be carrying the mod or anything related to the previous buggy nature, this is an intentional addition to the game, albeit a hidden one.)