How to replace multiple strings in a txt file and keep the original format

Hi all, my problem is how to replace multiple strings in a txt file and keep its original format; the original file is

Section = 1

*Lookhere

10

Dont Lookhere

Section = 2

*Lookhere

20

Dont Lookhere

the post changed file is

Section = 1

*Lookhere

1000

Dont Lookhere

Section = 2

*Lookhere

2000

Dont Lookhere

So i must localize the n (* Lookhere) argument and i read the n numbers just after this argument and i store them in a vector to change them via a function (*100 for example) and i re write the file with the same original format

Tanks at advance