I'm trying to do an oil change. Drained the oil, but I am unable to loosen the housing for the filter. (Mechanic put it on too tight when I had them do the head rebuild.) No options but to wait until I can schedule for the mechanic. So, I replaced the oil, but left the filter. I replace oil (Mobil 1 synthetic) and filter religiously every 5000 miles. Can I go an extra 5000 miles on this filter (It's a Mann from FCP Euro), or should I shorten this interval, or is there another option someone can recommend?

So the factory recommended oil and filter change interval is 10,000 miles.
The Mann filter is a "Volvo" filter.

What's the problem?
There is no problem. Have your mechanic remove the filter housing and reinstall a new filter and not tighten it so much. Ask him to pay for the oil that is lost during the oil filter change.
There is no need to "re-change" the oil at this point or even when he changes the filter as long as it's within the next 5,000 miles.

It will be fine.

Synthetic and the filter are good for 7500-10,000 miles. No sweat! Just do not crack the plastic...
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Keeping it running is better than buying new

You need a special tool for removing those plastic housings, if you intent to do the oil changes just buy the tool.

Would say with your oil change routine and regular use of synthetic, your car should be fine. When you do get it into the mechanic, have him change the oil and filter and he owes you a new filter housing if the overtightened filter housing cracks or breaks during removal!

A redeeming feature of synthetic oil is that it can run well beyond factory oil change intervals, so you’re most likely not in a situation that requires immediate attention.