Yes, you can easily replace just the rubber cover. I had to take mine off last year to replace a collapsed bumper strut. At the moment I don't recall exactly what I had to do to get it off, just that the whole procedure - remove rubber cover, remove aluminum bumper, remove strut, install new strut, replace aluminum bumper, replace rubber cover - took well under an hour. And, I did not know what to do when I started, so I was looking around an learning as I went, and working very slowly.

You may need two people to put the rubber cover back on: mine is a 1991, and the rubber cover has tongues that slide into a groove on each side, where it wraps around the side of the front fender, by the wheel wells. Both tongues have to be lined up in their respective grooves as you push the rubber cover into place. Weight is not the problem, but having a pair of eyes and hands on each side of the car guiding the cover on is. Otherwise it is a one man job. And you only need the second person for, literally, 5 to 10 seconds.
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)