But this would make the perfect opportunity to get the states off the federal dole. Want to assert your independence, pass a SYG law and tell the fed to go f@#$ itself.
That's perfectly permissible. The feds would laugh all the way to the bank, because they get to keep money that's not theirs in the first place. Yes, you have to abolish the grants, but you also have to remove that amount from their revenue stream and give it back to the people, who can then vote to send it (all of it, free of federal skim and liberty-slashing strings) to their states to do the stuff that it was to fund, IF THEY WANT TO. The feds, by offering it in this way, have tacitly admitted they have that much excess over the amount necessary to complete Constitutionally mandated federal duties, so their possession of this money proves you've been overtaxed.