I don't find anything in the NT that indicates the believer can unseal themselves or does God unseal the believer.
In fact the opposite. Romans 11:29: for Gods gifts and his call are irrevocable. Not much wiggle room there
Yep!
That seal is forever! You cannot undo what God has done. Period!
Ephesians 1:13-14
Ephesians 4:30
2 Corinthians 1:22
The burden is to prove your premise, that a seal cannot be broken by denial of what appropriated it.
I don't find anything in the NT that indicates the believer can unseal themselves or does God unseal the believer.
Then we are faced with the extraordinary feat of explaining away all the texts such as warn believers as believers against having an evil heart of unbelief in departing from the living God, drawing back unto perdition, back into bondage, making Christ of no effect, to no profit, falling from grace, etc., (Hebrews 3:12; Hebrews 10:38,39; Galatians 5:1-5) thus forfeiting what faith appropriated .
We cannot rationally argue that these warnings were contextually to unbelievers any more than we can argue that all such never were regenerate, while arguing that such warnings fall show of eternal damnation or are merely hypothetical is rather dubious.