Script to parse and update a parameter file

Dear All-

My requirement is as below, need your inputs please

1]
I have a file name Param.txt which contains the below data
#GLOBAL#
PARAM_VALUE=N

.............
............
CTRY=UK
.........

2] Next, I want to write a script which will check for some condition (lets assume checking count of records in a file). Once this condition is success, the script should read Param.txt, parse this file to find #GLOBAL#, and find the parameter "PARAM_VALUE" and then change the value of this from N to Y.
Thus post running of this script, it should ideally update value of parameter value within a file (from N to Y in this case)

Please help me with this script..

Thanks in advance

Suresh

---------- Post updated at 11:08 PM ---------- Previous update was at 12:03 PM ----------

Dear all, any inputs on this ?

Does your shell support sed -i option???