what i did .. i created a tool palettes folder on our network drive ...got my I.T to make it a read only folder for everyone but myself so that you can be the only one to edit the palette, if you dont then anyone can alter the blocks and screw them up , if this is done correctly then the pallete users will have a lock symbol on the bottom of their tool pallete screen when they install it , you obv wont ... create and build your libary of block and store all your blocks etc in your tool palettes folder (i had individual drawings with blocks on for each palette tab and stored them all in one folder which i called my ''build folder''.... start building your tool palette tabs the way you want them to be and look by dragging the blocks from your drawings to your individual tabs...once completed you can then give the rest of the users the tool palettes by linking them to your ''build folder'' file via options/files/tool palette file locations.
massive tip : when altering anything on your tool palette tab in order for your users to see the palette tab the same way as you see it. i do a ctrl-A , Ctrl-C , Ctrl-X, Ctrl-V on the tab , basically you copying , deleting and pasting it back onto your tab , if you didnt do that then whatever change you made will go to the bottom of the screen for the other users ..this basically keeps everything in the order you want it to be.
and to answer your question if youre using the export / import method then after you have made the changes you would need to export and import the file again for the changes to take affect.. this is really a longer method to sharing tool palettes and from what i understand its only best if the users you are sharing with are not on your network drive. if you are all using the same network drive then the method explained above is a quicker method to share and update for all users.