I think it will depend on how closely they look at the application. Organising exhibitions etc in Thailand itself would seem to be outside the remit of the DTV as you will have to deal with Thai companies, organisations and people in Thailand. Good luck and hopefully they do not scrutinise your statement too closely.
But the immigration have your record of leaving the country. Whatever, there is no need to show a TM30 when entering the country. I think yiu are totally misunderstanding what the TM30 is. Just forget about the TM30 till you reregister. You are both overthinking and over complicating matters.
You can show a hotel booking but that is not a TM30. A TM30 is registered within 24 hours of you arriving at accommodation. A hotel cannot register you till you check in. The TM30 you had is not valid now.
This is another it depends on the Immigration Office. In Jomtien I never had to have TM30 resubmitted after any travel returning to same address. At least it never interfered with any immigration interactions such as 90 Day reporting. However, in Chiang Mai my international travel means a new TM30 needs reporting upon return. No idea as yet regarding domestic.
Great service and the owner is a great guy. He does fret over the dress code at Govt offices. Lol Quite a few DTV people taking test with them when I was there.
I just got both car and bike license through these guys. They got residence cert, medical cert and gave package to take to DLT Changphuak Gate Driving School Chiang Mai