Please give examples for all the variations you want to transform.
According to my experience, the suggested measures do not quite fit the reality if the OP only tells what he thinks is relevant.
Also, it is not quite clear what you really want: do you want to fill the title tag (as the headline suggests) or do you want to rename the files as in the following you only talk about the filenames and that all the modifications should be performed on the filename - which is a little unusual.
If you want to import the part of the filename up to the underscore, then use the converter filename - tag and enter a mask like this:
%title%_%dummy%
This leaves out everything after the underscore - as you claim:
But I think that you want to replace the _ with "Chapter " - which is easily done with an action - see
/t/967/1
you then end up with data in the title tag that still has the number as head.
You can remove that (if it really is 2 characters wide) with an action of the type "format tag field" for TITLE and the format string
$cutleft(%title%,2).
You may then rename the files with the converter Tag-Filename.
But as I said: I am not sure, what you really want.