Montgomery Clift "re-scriptor" in new documentary?

[Phillyrich]

There is a new documentary film soon on dvd, entitled : "Making Montgomery Clift"
Leonard Maltin gives it a very favorable review.

Seems interesting not in the least, due to Clift's attempts at personal revision of his scripted dialogue.
(Wonder how his directors felt?)

I have often wondered how often actors changed (interfered?) with the written dialogue. I can
see John Wayne or Gary Cooper reducing dialogue to points of action. But adding your own words
to a script?

In the days when the studio/director was king, I wonder how much of actors revising their parts, was allowed?

https://leonardmaltin.com/making-montgomery-clift/

[silentfilm]

It depends on the director. Billy Wilder, who wrote the scripts to most of his films, insisted on the lines being used almost verbatim. On the other hand, Leo McCarey had started off making slapstick comedies at Hal Roach where everybody improvised on the set. Cary Grant was flummoxed making The Awful Truth (1937) because much of the dialog was improvised. There's an interesting short documentary on the Criterion blu-ray that goes into McCarey's working methods. He always had a piano on-set for inspiration.