Wrong information: this is from the Immigration Act:
Section 77: Any person who fails to comply with Section 38 shall be liable to a fine not exceeding two thousand baht. However, if such person is the manager of a hotel, he shall be liable to a fine of not less than two thousand baht and not exceeding ten thousand baht.
It is actually the whole page who explains that you can NOT make appointments based on the fact that the Thai Embassy in Malaysia is now using the on-line application website from the Thai Ministry Of Foreign Affairs, the link is several times mentioned, BUT special for you:
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So no walk to the Embassy, no need for appointments, no need to make hard copies to hand over, just visit the website while being in Malaysia and apply by sending in files and information.
You can NOT change from one visa to the DTV inside Thailand.
IF your visa is used you can leave the country before the Admitted until date and apply for a new DTV abroad.
OR if you are on an Extension of Stay permitted up to xx/xx/xx, than depending on reason of issue, you cancel this Extension of Stay, leave Thailand and apply for the DTV.