Bom and Cost Update

I have a few queries
Suppose I create a bom xxx/01 with materials
I submit the bom
now it is non editable
after a couple of months another process is added
I cannot edit this bom xxx/01
so I have to create another bom xxx/02
I add all the materials
I also add the new material
there is a cost difference between these two bom

this bom is used in another bom yyy/01
which will the bom yyy/01 take the default as
is it xxx/01 or xxx/02 ??
will it update the cost
Which is the best way to handle such a scenario ?
Please help

I believe yyy/01 will pull from whichever BOM is marked as default. Try going back and updating the cost of xxx/01.

Thanks for the reply Agerken
I have some more queries
Why am I not able to delete a bom that is inactive ?
What if I make both xxx/01 and xxx/02 active and default ?

I tried this scenario
if I make xxx/01 ---- inactive and non default
xxx/02 — active and default
even then
yyy/01 is not updating the cost of xxx/02