Guessing, but... Media Views in Theater View (and Media Network) are part of the Library. You can only alter the Library from the Server machine, otherwise any changes made are lost when you close and restart the client. This does not apply to Theater View skinning and other options in the
Tools > Options > Theater View panel, but you can't change any of the Views in that dialog from a client.
Are you trying to make these edits on a client of another Media Server?
Also, for the record, substring searches are relatively slow operations (not horrible, but slower than some). Because of this, and because they can be fragile (they don't persist if you re-arrange your disk structure), it is usually best to limit [Filename] contains type searches where possible in your media views. Stacking many of them can make a view slow to open and refresh.
If you need to parse the filename for some kind of metadata, you can usually accomplish the same thing, better, by using a
Tag on Import rule to apply a tag to the files in question at import. Then the substring search only needs to happen once at Import time, rather than for each file in the View every single time you open or refresh it.