Honestly, it's not that hard to take off the bumper. I'd say the whole thing (taking off the bumper and replacing the lights, then putting it all back together) shouldn't take more than an hour.. maybe two if you really have no idea what you're doing. Just use an installs guide and it should be a piece of cake.
With all the time you'll spend trying to do it without removing the bumper (feeling around and trying to bend back the underbody plastics), you could've already had it done by just taking off the bumper and being able to see what you're doing. My $.02.
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