The ability for the upgrade to have Chaos Power spell override would, IMO, be a little too strong. Think of all the 1 quanta creature-target spells that could come out from 1 Supernova. A bit scary.
If it's not that big of a deal I may change the upgrade to Chaos Power but decrease its stats a bit.
In its current state, I agree that it would probably be too powerful if you flat out changed from chaos seed to chaos power on upped.
Some possible alternatives:
1) Lower stats on upped to compensate
2) Make it a probability to be either chaos seed or chaos power ... maybe 50/50 or 75/25...
3) do number 2 for both, but have a better chaos power chance for upped.