In my old passport (still valid for about 1 year), there is a valid extended period of stay based on a Non O/retirement visa and a re-entry permit. My plan is to get a new passport issued in my home country where I am now. Can I just return to Thailand without any problems entering Thailand? Thanks for advice..

Yes, once in Thailand you can get the visa stamps transferred

If main page and the Thai immigration stamps/stickers on the old passport are "unharmed" you will have no problem.

Different countries have different methods of voiding an old passport.

Some put void stamps on all EMPTY pages others just punch holes.

33 minutes ago, scubascuba3 said:

Yes, once in Thailand you can get the visa stamps transferred

Visas are not transfered. 

28 minutes ago, KhunBENQ said:

If main page and the Thai immigration stamps/stickers on the old passport are "unharmed" you will have no problem.

Different countries have different methods of voiding an old passport.

Some put void stamps on all EMPTY pages others just punch holes.

Then just show the old and new passports and immigration at airport will stamp my new period of stay  in the new passport? I never did this before...

13 minutes ago, Sjoerd said:

Then just show the old and new passports and immigration at airport will stamp my new period of stay  in the new passport? I never did this before...

Yes, that's exactly how it works. Once entered, then go to your immigration office and they will transfer the visa/extension and re-entry permit. Should be no charge but you never know with some offices.

 

I did just that last year and wrote about my experience here:

 

I should just add that, in Belgium, they cut the corners of every page of the old passport. However, I explained that the relevant "Thai stamp" pages (conversion to Non O, last extension, re-entry permit...) should be left intact, I clearly marked them with tape, and they accepted without any question.