@Ly ************
, you;re mixing up terminology and that's causing problems with the answers you're getting.
You EXTEND visas at the immigration offices inside the country. and at a thai consulate in another country you get a NEW visa entirely.
SO what you're wanting to do is BUY another 90 day single entry Non-B visa from the thai consulate in Penang.
What is the reason that the invitation letter is addressed to the consulate in Kuala Lumpur and not where you want to go apply for the visa?
AFAIK: the documentation has to be addressed to the consulate you're applying at ..