We have offered these for many years. Couple of points to consider.....
Remember to include in your TISAs that it is a variable rate product, because by allowing rate bump, it becomes one. Also, you should make it clear that a rate bump is allowed during the initial term only (not on sucessive renewals of the CD). Then get customer to initial and date when they exercise the rate bump (and obviously you change you computer to the new rate).
Our experience is that we shave the rate going in, because customers think it is such a good deal they will take a lower rate than the current market and then, the good news for the bank is that 99% NEVER return to ask you about bumping their rate during the term! It's a win-win.
Good luck.