Yes, Thai citizens can extend their Laos visa. However, you may only extend your visa twice and remain for a maximum of 90 days.

To extend your visa, you will need to visit the Immigration Department in Vientiane or the Immigration Division Office in the province where you are staying. You will need to bring your passport, your visa, and a copy of your passport-size photograph.

The first extension of your visa is 30 USD, and the second extension costs 60 USD. Processing time is typically 1-2 days.

Here are the requirements for extending a Laos visa for Thai citizens:

A valid passport is valid for at least six months beyond the scheduled departure date from Laos.
Your most recent visa.
A duplicate of your passport-size picture.
A visa extension application form has been completed.
There is a cost of $30 for the first extension and $60 for the second.

If you intend to renew your visa, I recommend that you apply at least 10 days before your visa expires. This will allow you to complete your application and prevent any last-minute issues.