Could a past actor every make a return in a future film?

It's already happened before.

Charles Gray played Dikko Henderson in YOLT and Ernst Stavro Blofeld in DAF.

Joe Don Baker played Brad Whitaker in TLD and Jack Wade in GOLDENEYE and TND.

So I would expect that it depends upon the individual actor and the individual role.

ant-mac

Timothy Dalton could return as an older Bond. It would be epic.

Christopher Walken. I'm not saying no. But why not go with John Malkovich?

I'm motivated by my Duty.

It has been done before. As long as it isnt an actual previous Bond, I am sure people wouldnt have an issue.

I actually proposed Walken's return a while back, I think it would be cool to have him as the director of the CIA.

As others have said, the franchise has a long history of returning actors and after the reboot pretty much everyone is open. My own personal stipulation would be to always invert the vectors of good and evil; villain return as allies and allies return as villains.

It takes all the running you can do, to keep in the same place.