I'm cleaning my engine bay also. I tried to use needle nose pliers to squeeze the plastic pin together but the pin broke off (maybe 30 year old plastic). Since they are behind the metal flange, i just taped them up and painted around them. Not concourse, but I found these on Amazon by searching for 'push mount releasable cable tie' -
https://www.amazon.com/Uxcell-Nylon-Releasable-Mount-Length/dp/B00UYSJU1S
I didn't buy them so make sure he size is right.
Mike