HP 16C repair

[fraxvo]

Hello,
I was trying to repair an HP 16C calculator which my father gave me a long time ago as a gift.
Its logic works., but some areas of the display work only if you push really hard near it, I guess it has to do with deteriorated connections to the display. (Image on the bottom, they are all 8s in hex mode)
I decided to open it by removing the rubber feet and unscrewing where needed.
I encountered a roadblock, though. According to Opening a Voyager I have to remove some black nubs (the guide calls them heat stakes).
Is there a less destructive alternative to it?
If there isn't, can I replace those black nubs with some screws instead of melting them on?
Thanks in advance.

P.S. is there any way to do some SIN COS TAN on it?