Tax the property of the former slave plantation owners.
They would be unable to pay the tax. Indeed many couldn't even OTL, so that large amounts of lad was auctioned off for unpaid taxes.
So all you'd end up doing is replacing one set of planters by another. and even if the latter mostly came from the North, most of them would probably soon "assimilate" and adopt the same racial attitudes as the locals- if indeed they didn't hold such views already. Racism was the norm in those days, not the exception.
Anyway how does any of this help Grant's reputation? He is till pursuing what will be seen as a punitive reconstruction policy, and when it fails (a virtual certainty) his reputation will suffer accordingly.
Imho the big difficulty about this WI is that it's darned difficult to enhance Grant's reputation both for contemporaries and for posterity. If he rejects Radical Reconstruction, and leaves the South under white rule, he will be praised for his leniency to the fallen foe - by most people at the time. But 21C observers won't be so pleased. OTOH, if he tries to achieve racial equality (and inevitably fails), he will get brownie points from 21C observers for his gallant attempt, but at the time, and for generations to come, he will be seen as both vindictive and a failure.
Lincoln avoided this dilemma by getting assassinated at precisely the right moment. So perhaps Grant's best bet is to die suddenly right after the 1872 election, while his reconstruction policies still seem to be working, so that their ultimate failure gets blamed on hi successors.