AppleScript: Bulk iTunes work-and-movement
Use is in to check whether " I." is inside song name, like this: if " I." is in someString.

Use the offset command to get  its position inside of the song name



Here's is an example

set songName to (get name of thisTrack)
if " I." is in songName then -- " I." is inside this song name
    set {theWork, theMovement} to my splitText(songName, " I.") -- split the string to get the Work and the Movement
end if


on splitText(t, theSearchString)
    set x to the offset of theSearchString in t
    set a to text 1 thru (x - 1) of t -- everything before theSearchString would be set as the work
    set b to text x thru -1 of t -- this part would be set as the movement
    return {a, b}
end splitText