Concentration-gating. What do you think?

[Quertus]

Well there's that free willed bit... If your undead or constructs are programmable you don't have to concentrate, but you also don't get to change their orders as an act of will.

Program Undead spell, instantaneous duration? Necrohacking is a thing now!

Given that Command Undead is only, what, level 2, lasts for day/level, and works on sentient undead, too? This sounds like a Cantrip at most, and an essential one for commanding undead laborers.

The tricky part is getting the Construct version of this spell balanced just right. Maybe a Canrip works for Constructs you created, or ones you've "hacked", and the "hacking" part is the higher-level spell? (See also... Rod of Construct Control?)

- The recipient of a buff has a number of slots equal to 5+Cha mod worth of spell levels they can support.

It occurs to me that this is a stealth buff (heh) for classes that can go book-diving for lower-level versions of spells, like... Archivist and Artificer?