Split one tag into two fields

How do I split a tag from one field to another? by checking

For example.

I have "50 cent feat Young buck" in my Artist field but I want Mp3Tag to read this and split it so it writes

"50 cent" to the artist and "feat young buck" to another tag

Try an action of the type "Guess value" for ARTIST
Enter as guessing pattern:
%artist% feat %another tag%
This leaves out the "feat" but that should be easy to add to the %another tag% field with a format value action.

Just a personal note:
The tag is all the metadata. The tag can follow certain conventions and usually is described as V1 tag or OGG or FLAC tag.
A tag then consists of fields.
I assumed that you wanted to split one field into several others.