All are ok?
If I could, I'd have done it already.
If I could, I'd have chosen a different job.
If I could, I'd have divorced his/her a long time ago.

Question

Answer

Of course, al of your examples are contractions. To my American ear they sound a little weird without two "haves." - 
If I could have, I would have done it already.
Or,

If I couldda, I wouldda done it already. That's how I wouldda said it.

Answer

I agree with the above but the title should read Are these ok?All are ok isnt really a question more a statement implying that they are correct without question.Hope this helps

Answer

The only problem is in your third example.  It should say "him/her" not "his/her".  Otherwise, all are okay.

Answer

Everything is correct except this:

"If I could, I'd have divorced his/her a long time ago."

In this sentence, "his" should be "him".  Remember that "his" is possessive.  "I like HIS shirt".

So, the correct phrase would be:

"If I could, I'd have divorced him/her a long time ago."

Everything else is perfect!  Good job!

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