I am returning to my employer (worked there for almost 10 years and left on good terms with a stellar employment record) after being gone for about 8 years. I am about six weeks short of the probationary period ending, which will reinstate all my past years of experience. I will miss this year's performance bonus on that basis (that my probationary period doesn't end for six weeks). I will get the cost of living adjustment but not the performance pay. Is there precedent for reducing the probationary period? Should I ask for that?
If you have a good professional rapport with your boss you don't need a precedent, you just need to ask. You could by all means explain why you think you should get the bonus.
But on the flipside be prepared for an answer along the lines of: the bonus is for people who put in a whole years work, you've only been back for X weeks and it wouldn't be fair to the others if you got the same bonus as them, sorry. If you get this response you could also expect your rapport to be slightly harmed as your boss might think you have an "entitled" attitude.
Personally I'd just wait for next year.
You should definitely ask but it would be unusual for the probationary period to be shortened.
The probationary period in a company is usually written into a company policy. For an exception to be made, the policy would need to be revised, rewritten, reviewed, approved etc. etc. Unless your company is unusually far-sighted, they won't have allowed for different length of probationary period.
Give it a go, the worst that can happen is they say no, but don't expect a yes.