the only time I've ever heard someone replced a banjo head (especially the plastic ones) is when the head burst or they wanted a different sound. I'd be curious to know if there were other things to consider.
If I remember the scruggs book right he said you checked the head tension by pressing on it with you hand. I'm not sure a tork wrench would be a good idea.
Here is the info I have & Im pretty sure this is from the scruggs book (I only have the one page)
..."tighten the brackets a little at a time, proceeding clockwise, and keep repeating the process until the head is tightened to the proper degree. Watch the bridge closely, and when it is standing fairly level, the head is about as tight as it will go without bursting. There should not be any loose brackets when the head is tightened. Another check is to look at the tension hoop. It should be level all away around the shell..."
Charcloth