How to allow cantrips to be changed

The wizard in my game has requested the ability to change out his cantrips similarly to his higher level spells. His justification is that every other wizard spell is memorizable, so having fixed spells seems antithetical. I kind of agree with him.

I know that there is no mechanism for changing cantrips, but I’m trying to come up with a fair means of doing so.

The two extremes, as I see it, are:

  1. Cantrips can be swapped out just like preparing any other spell.
  2. Retrain a the cantrip, taking 250 days of Downtime, as if learning a new skill.

I’m interested in having a good middle ground option, patterned on other rules, if possible.

Here’s the house rules I have tentatively decided on. Critiques welcomed.

Cantrip House Rules

For all following rules, when using a cantrip that you don’t currently “know”, for classes that use a spell book, the cantrip must be in the spell book. Cantrips count as 1st level spells for purposes of price and scribing.

  • When you gain a level, you may swap one cantrip for another that you have available.

  • As a Downtime Activity, a cantrip can be swapped for another that you have available after 10 days of practice and the expenditure of 20gp.

  • Cantrips can be prepared and cast as 1st level spells. If the cantrip effects improve with level, the spell slot used to cast it must be 2 levels higher per step of improvement.

  • Cantrips can be cast as rituals. The cantrip improves with level as normal.

As with any house rule, I reserve the right to change it if it breaks.

Be warned! My DMing style is quite liberal. If you use this, wizards, druids, & clerics in your group may become unbalanced.