All good, everything can be changed in a contract but PE won't stick and artifacts won't let you claim. Here is an example:
as you can see I changed the reward, amount, amount of eggs needed, my eggs delivered and I was able to claim all of the rewards but upon returning to my home farm the PE was corrected.
if you want to try search amountofeggsrequired:reward amount:: as Edouble
example 150000000000000000;3::
You can also add the value for reward type in the middle if you know them, they are dword and boosts are 9 so you can do it like this for this contract in my example
400000000000000;9D;1::
29000000000000000;9D;1::
150000000000000000;9D;3::
PE is 4
Boost token is 7 and I can't remember the rest but you can try values 1-30 to see them all