P_ExecutiveOverride(variable, value)
This is a Lua function for someone who is pushing up against the limitations of the SRB2 engine and is unwilling to compromise in persuit of their goal. It forces a given variable to be set to a desired value at the end of the tic, after the game's finished doing everything else it wants to do but just before rendering. This could be feasibly handled as a FIFO queue which is run through once all other thinker logic has been completed.
In the (relatively) safe, sanitised and orderly behaviour of Lua scripts as they currently are, various checks run on certain variables at the end of the tic. This can lead to instances where some variables are effectively unable to be modified, such as the height of MT_PLAYER (continuously adjusted for scale and whether they're spinning or not) or the object flag MF_UNDERWATER, which is forcibly set at the end of each tic depending on whether an object is submerged in liquid or not. Whenever a problem occurs, a nice little error message pops up in the console and the hook is removed. I think it's fair to say that this idea is one way of getting past the fundamental issue of trying to take full control without the full cooperation of the engine.
With P_ExecutiveOverride, there are some real cracking things possible. Want to create flowing water from a bunch of connected transparent mobjs, but can't seem to make objects behave like they're underwater? P_ExecutiveOverride(toucher.flags, $1|MF_UNDERWATER) in a MobjCollide hook (once z is taken into consideration). Want to give a player every shield at once? Want to force an object below the floor height of a sector? Want to make a player turning super behave like the NiGHTS Super Sonic? If you're using this function, we're going to assume you know what you're doing and are wholly responsible for whatever godless/godly abomination you create.
If it's a variable stored in srb2 and the userdata required to access it is avaiable to you, it's yours and yours alone to set for the rest of the tic- no need to fight the game for what's rightfully yours.