Am replacing thermostate. Housing is a deep well and hard to get to gasket. when removing hose housing old gasket seems to be OK still in tack. Can I reuse it and can I place new gasket over top of old?

if you do that,you are/will be most likely taking a very good chance of doing this job again.it may be hard to get to.but if it leaks,it will still be hard to get to.do it right the first time and you won't have to worry about it maybe or maybe not leaking.