Go to line starting with and variable not detected

[Gribouillis]

In your code, it seems that new_name is only defined if some conditions have occurred: a line starting with /54/ is needed before, and num in pj needs to be satisfied, perhaps other conditions that we don't see. The error probably means that some of these necessary conditions failed. You could perhaps write

new_name = 'DEFAULT_NAME'

at the top of the file to see if this name is used.