CB currently sells alternate "skins" in metal of four of the characters in the CoreSet. I have used hexagon bases for them. I have also painted hexagon bases as proxies for use in casual games.
git checkout -b hexagon_branch master git commit -a -m "New hexagon base" git rebase Just kidding, I found a couple examples on youtube on how you can do it. Pinning your miniature would be the recommended way, it provides better stability to the miniature but it's also very careful work: Fast and dirty, just cut and glue, I assume this will work for most of the miniatures, but I can see how it can be a problem for Gata or Parvati alt where you have such a tiny space to work on: Overall, I suggest asking this question at this forum: https://forum.corvusbelli.com/forums/miniatures.109/ I'm sure they'll be more helpful than I am.
I've rebased all my Aristeia minis, because I wanted texture on my base. The textures are done with Green Stuff World rolling pins. I remove the plastic minis carefully (easy in most of the case with a good blade), then glue the mini on the greenstuff with superglue. The plastic mini are so lightweight that it is normally enough. Pinning may also be a solution in some case.