This guide explain how a better way to lock specific forms you would like to have on the wheel.
Guide to Customize the Transform Wheel
Unfortunately it’s not possible to edit the layout of the form wheel atm. Maybe devs improve this after high amount of requests.
But there is a workaround to have it not ‘randomly’ change character. Not ideal but it’s better than nothing.
The character that gets removed from the wheel is the one you have switched to least recently.
You can force a specific character to swap out of your wheel by sequentially transforming to the other 7 characters on you wheel (the ones you want to keep in the wheel) before using the tree menu to select the new transformation.