WildWords is sufficiently flexible to play a game with the added rule that every word must be related to a particular topic. You won't score as many points or use all seven tiles as often, but a themed game can add amusement or educational value or both.

When playing a themed game, consider adding the six spare tiles to the pot. Use them just like wild tiles to increase the chances of playing interesting words related to the theme.

Since a play may form a number of new words, just insist that the main word formed be related to the theme.

If the playing of a word has consequences (other than points), require that each play use at least four tiles. For example, in a chores assignment game, V* would be too easy of a play to force your opponent to do the vacuuming. But V*UM should do it.

I once played a game with the condition that every word had to be (in some small way) related to a particular person who was driving all the players nuts. It produced a fair number of laughs around the board and was somewhat psychotherapeutic.

You can also pick a theme that's educational. Be creative. That's what WildWords is about.