That's a good suggestion, yeah I should put something like that together at some point. Until then though, if you grab Slade: https://github.com/sirjuddington/SLADE/releases
open OHM, select the graphics you want palettized, then hit the little blue square/red circle icon at the top right, choose "png/truecolor" and that'll convert em all for you.
(Slade should have a lil dropdown menu under the file listings which will let you view all graphics files, that'd help save you some time)