Is it possible to extend a visa exempt stamp by 30 days and then apply for a 7-day extension in Thailand?

@Lea***

nope, that stamp will not in any way shape or form affect your future ability to get visas or enter thailand. You can only extend a 30 day visa exempt or tourist visa entry ONCE for 30 days. The only thing available to you after that is the extension denied 7 day stamp to "get out of dodge". You'll be fine.

BUT

Remember, while the 30 day extension stamp is ADDED to your current expiration date when you get it, the 7 day stamp starts from the date you apply for it. SO wait until your 30 day extension is running out before getting it so you don't lose any days left on your extension.