Replace certain location with "N" in File

I have two big files and the simplified version looks like this:

File1:

>Header1
 AAAAAAAACCCCCCTAAAAAAAAA
>Header3
 AAAAAAAACCCCCCTAAAAAAAAA
>Header10
 CCCCCCCCCCCCCCAAACCCCCCC
>Header2
 CCCCCCCCCCCCCCAAACCCCCCC

In File2, the 1st line means 2nd character under Header1. The 2nd line means 8th character under Header3. So on. In my output, I want to replace the 2nd character under Header1, 8th character under Header3, and 5th character under Header2 by "N".

File2:

Header1 2
Header3 8
Header2 5

Output Expected:

>Header1
 ANAANAAACCCCCCTAAAAAAAAA
>Header3
 AAAAAAANCCCCCCTAAAAAAAAA
>Header10
 CCCCCCCCCCCCCCAAACCCCCCC
>Header2
 CCCCNCCCCCCCCCAAACCCCCCC

Can you tell me how can I do it?