I think the cleanest thing would be to create a custom macro to replace the tag display you have.
So now you have something like:
<%# BlogFunctions.GetDocumentTags(Eval("DocumentTagGroupID"), Eval("DocumentTags"), "/") %>
And update it to something like:
<%# GetBetterTags(Eval("DocumentTagGroupID"), Eval("DocumentTags"), "/") %>
In the api examples of the documentation you can find how to retrieve tag information:
For quick results you could go for a
.Replace(...) as suggested by the 2nd comment from Brenden here: https://devnet.kentico.com/questions/blogfunctions-getdocumenttags()-not-working. But guess in you're case that might be getting a bit to complicated.