If you have lots of files with separators such as the underscore, searching on file names or titles does not work well. Is the best solution to replace the underscore with a space? Batch changes are not intended for that I think. Neither did File Replacement do the job after selecting multiple files - all options except Find were grayed out. I can separate out those files with an underscore, but what next?
Could you give a specific example? I just tried a file named “foo_bar_baz.pdf”, and I was able to find it by searching for “foo”, “bar”, or “baz”. This works because I have Match Partial Words turned on.
If you don’t want to use Match Partial Words, you could replace the underscores with spaces so that EagleFiler sees them as separate words.