He's not going to change passports, that's ridiculous. Then pay 8,500 for agent to re-enter at BKK Airport. Your plan to enter via Laos with an agent should be fine. 'Generally' you get 2 land border entries per calendar year - regardless of your previous history. I had a TR visa and 5 covid extensions and used an agent to do a land bounce, no problems whatsoever.
Visa Exemption - on arrival You get 45+30 now so 75 days vs. 90 on TR 60+30. Come in on Visa exemption and see what they say. Also note you can get 2x border runs to Cambodia/ calender year, regardless of your recent history, this is guaranteed if you use an agent such as Thai Visa SErvice out of BKK.
Edited:If you make it thru on a Visa Exempt then get your 30 day extension here-> then use a Visa agent out of Bangkok such as Thai Visa Service to do a border bounce to Cambodia to repeat the process. This agent will secure you another Visa Exempt up to a maximum of 2/calendar year, as it will be 2023 by then you are good to go on this option.
One day is enough. If you have many stamps and long stay here as a tourist I would recommend using a Visa Company from Pattaya. Avoid Poipet border crossing.