Q1: If frame 60 is your last frame, you can add more to the end, copy the keyframe, paste it at the end and then delete the keyframe at 60. That by far is the easiest way. If you have more actions on the end, you can always do the same thing by changing the length to make some space and move the end bits over. You can copy and paste entire frames via the keyframe editor (key icon bottom right hand side).
Poser also has a "retime animation" ability but if the part you want to retime is in the middle, it will overwrite the keyframes at the end. So if you want to change the action from 30 - 60 to 30-70 it'll overwrite whatever movements you had from 60 - whatever the next keyframe is. So you'll have to move the end keyframes over anyways.
As a side note, with having keyframes only at 30 and 60, you are going to have some issues when uploading. SL's optimization throws out frames when you haven't moved the figure enough or when the keyframes aren't closer together. If you are animating at 30fps, I'd retime the entire animation down to 15fps.
This is actually where retiming would work. If you were happy about the timing of the animation, you could drop the fps to 15 and then retime say frame 2-300 to 2-150. (Remember frame 1 needs to be the default T pose). But since you want more space, you can change the frame rate in the keyframe editor, then copy and paste the keyframes 1/2 the amount closer together while still giving room for a larger gap between the origional frames 30 and 60.
Animating at 15fps gives you much more leeway in slower and/or smoother animations by tricking the optimization process. If you have a pause that SL throws out at 30fps, even the same length time wise at 15fps SL will keep it in because the keyframes appear to be closer.
Q2: I haven't had any issues with Poser freezing when copying paramaters from 1 side to the other, mostly because I haven't tried it more than once. The bigger issue with symmetry is that on one side the degrees will be in the negative but the other arm will be in the positive. It's not for every single axis nor for each joint. Personally I just write the paramaters down and type in each with changing to the negative if I see it move in the wrong direction. But that's probably not the optimal way of working
