The easiest option, if you're comfortable with having no regeneration at all, would be to give yourself an ability with the Stunted Magicka effect. It's the effect which prevents the Atronach birthsign from regenerating magicka. You can do this at the console by typing:
player.SetAV StuntedMagicka 1The settings for magicka regeneration apply to NPCs and spellcasting creatures as well as the PC. Without a complete redesign of enemy spellcasters and AI, simply turning off magicka regeneration would cripple them. I believe Race Balancing Project's regeneration settings are zero or near-zero at low Willpower values, but it also greatly increases the size of your (and NPCs') magicka pool.
More detailed control can be had with scripts. For instance, with nGCD I disabled vanilla magicka regeneration completely then added a script to all actors which regenerates magicka based on a completely different formula. If you just want to lower the player's regeneration, it might be simpler to leave the normal formula in place but add a script which
reduces your Magicka at a fixed rate.
Anyway, there are definitely options.