How to you guys install modifications or work on your bike without a garage?

You can rent storage space and use it like a garage. Probably could find something for as low as $40-ish a month.

If you have a town house, wheel it in thru the back gate to your property off common ground. Or just take it the extra 50 feet to the nearest public road. There might be a law where you live but I doubt you'd be held accountable for it, as long as you're respectful and obay any police that asks you to stop I can't see it being a problem.

I've proped up a bike on stands on public roads before without issue. If you're not blocking trafic or otherwise endangering people everyone will usually just ignore you.

Also might be worth diging up the bi-laws and fighting them on the fine. Most HOAs have spesific wording excusing 1st time offenses.

i live in a hoa and i can tinker with no issues