I had to look that up. That looks to be a DM's Guild product? If so, it's not available on Roll20, but should be soon, as work on the partnership grows. In the meantime, everything on your sheet is editable. Just pick the closest one during charactermancer creation, and then manually edit anything after the character is saved. Charactermancer level up never references background, only the creator does, so there should be no conflicts or issues arising from this. In general, once your character is created, you can edit it to your heart's content, only spells are occasionally messed with--if you do any swapping out on levelup, it might overwrite any custom changes on those spells. Once the Player Primer becomes Roll20-available, the level of integration with the charactermancer and compendium will likely be dependent on the authors. It's extra work to put in, and up to them to decide if that has sufficient value to justify it.