Well adding passport pages is no longer offered by the embassy.
For my last passport renewal in Thailand this is what I did.
Attended the Pattaya consular outreach (which is of course finished now) and handed in my passport renewal application, picture, and fee.
When it was ready, I was emailed, and then I went to the embassy in Bangkok to pick it up (along with the old passport and embassy letter) at the intake window in front of the building.
I liked that method very much. But that is the past.
Cheers.