We know too little of physics to know whether it is indeed possible to change the cosmological constants to defeat a false vacuum collapse (which, also, is just theoretical), much less determine how to do it.
In Egan's Schild's Ladder, the expansion of the Void cannot be thwarted, but it is possible to "reprogram" matter and colonize the Void itself.
One possible way to set up the effect you describe might be to build a dense shell of neutronium or hide inside a event horizon (the latter strategy, for different purposes, is described in the Heechee series).
You must take into account that our very existence is tied to most of those universal constants, so manipulating them on large scales would be both exceedingly difficult and tremendously dangerous. This is one of the plot points in the Duchy of Terra series, where
it turns out that the Ancients, before known Galactic history, did change some of those constants on a galactic scale to vastly improve the efficiency of their stardrive. Unfortunately, one of the side effects was to kill most forms of life in the Galaxy, themselves included, until other forms of life could evolve that were compatible with the new constants.
As for the expansion speed of the vacuum collapse, it's anyone's guess. The hypothesis that it would proceed at the speed of light is just this -- a hypothesis. Since it would be a phase change in the space vacuum, it could expand at any speed between zero and c. For instance, sodium acetate trihydrate crystallisation does not proceed at the speed of sound in water, but rather quite slowly (the speed of water freezing, which can be quite high, is actually a phase speed and proceeds usually at the speed of the wind. There's one extreme and possibly incorrect instance (Hector Servadac: Travels and Adventures Through the Solar System by Jules Verne) in which it is pictured proceeding at the speed of sound in water.