1: During Creation
Perhaps, either for ease or as a placeholder for the below idea, a warning or similar if you go to change Generation that values for XP spent on your sheet may be broken now and you should probably start over and begin with Generation. A little notice at the bottom of Character Creation directing you to go straight to Generation if you want to adjust it might also be a good idea.
With Character Creation, spending XP on Generation should be the first thing able to be done so that all actual costs are properly reflected. Maybe allowing XP to be spent on it on the initial Creation page similar to the way Merits and Flaws are done or going straight from the initial Creation page to the Generation Backgrounds page with a note that it must be done first.
2: After Creation
Similarly, Diablerists, especially from Sabbat settings where it is far more common, have incorrect costs for many things such as Skills and Backgrounds once their generation increases, particularly when ascending from Neonate. Possibly adding a sort of "Lock XP spent at [X] Generation" so that when you increase your Generation it doesn't forcibly cause you to spend the new Generation's total cost for Skills/Backgrounds/et cetera, and instead just the amount you should.
Example: If you are a Neonate and have 1 dot in a Skill for a Total of 1 XP, then increase it to 2 dots, it costs 2 XP for a Total of 3 XP. If you were of a higher generation, the Total would instead be 6 XP. If you Diablerize and increase your Generation to Ancilla, then decide to increase that Skill to 3 dots, it should only cost 6 XP to increase, for a Total of 9 XP spent. However, the system calculates the Total cost based on your Generation, forcing you to spend an extra 3 XP to reach the Total cost of 12 XP as though you had purchased the entire Skill as an Ancilla.
1: During Creation Perhaps, either for ease or as a placeholder for the below idea, a warning or similar if you go to change Generation that values for XP spent on your sheet may be broken now and you should probably start over and begin with Generation. A little notice at the bottom of Character Creation directing you to go straight to Generation if you want to adjust it might also be a good idea.
With Character Creation, spending XP on Generation should be the first thing able to be done so that all actual costs are properly reflected. Maybe allowing XP to be spent on it on the initial Creation page similar to the way Merits and Flaws are done or going straight from the initial Creation page to the Generation Backgrounds page with a note that it must be done first.
2: After Creation Similarly, Diablerists, especially from Sabbat settings where it is far more common, have incorrect costs for many things such as Skills and Backgrounds once their generation increases, particularly when ascending from Neonate. Possibly adding a sort of "Lock XP spent at [X] Generation" so that when you increase your Generation it doesn't forcibly cause you to spend the new Generation's total cost for Skills/Backgrounds/et cetera, and instead just the amount you should.
Example: If you are a Neonate and have 1 dot in a Skill for a Total of 1 XP, then increase it to 2 dots, it costs 2 XP for a Total of 3 XP. If you were of a higher generation, the Total would instead be 6 XP. If you Diablerize and increase your Generation to Ancilla, then decide to increase that Skill to 3 dots, it should only cost 6 XP to increase, for a Total of 9 XP spent. However, the system calculates the Total cost based on your Generation, forcing you to spend an extra 3 XP to reach the Total cost of 12 XP as though you had purchased the entire Skill as an Ancilla.