Entering data fields in a table where rows have a hierarchy

Situation: A store is adding in how much money has been spent on products in their store that week. They can enter the figures either at the individual product level, or at the brand that product belongs to.

So, either at Nestlé level, or at KitKat, Milkybar, Aero...

I want to make sure the user has the flexibility to enter figures at whichever level of hierarchy they want, but also don't want to end up with duplicate or mismatching figures by someone entering in a value at Parent AND at each Child.

This is fine when they first start - we can just disable the Parent / Child field once they choose which level of the hierarchy for that product they're using.

HOWEVER, the issue I'm having is how can we allow the user to change which level they've been using? For various reasons they may need to change from a global Parent (Nestlé) figure to specifying a value for each product instead (or if they've done it at Child level (KitKat) they may want to actually just specify at Parent level instead).

I don't want to fill the fields with toggle icons as that's visually noisy. I don't want to add a global toggle for Parent / Child because there are many brands out there (Coca Cola, Mars etc) and the user may still wish to enter figures at child level for one brand but Parent level for another).

What is a simple method to allow the user to change from one level of hierarchy they've already specified up/down to the other level?

The only thought I currently have is that if the user clicks a Disabled field they will be given a prompt asking if they now wish to add figures at Child level, but that seems like an accessibility fail, and it isn't really that obvious that a disabled field can be clicked.