Lock specific columns in Table but still be able to add/delete rows?

First you will have to unblock each cell, select the whole table then press control+1-> Format Cell window will ope with this command->Go to the last tab protection->uncheck on locked then ok. Now select those column which one you are wishing to lock, do the same things as you did earlier for unlocking the cells, now this time you will have to check mark on locked cell.

Press Alt-H-O-P you will see a window protect sheet. You can give permission to the use ( list of permission will show you in window) and give the password for protection then.

Hope this will help you