substitute a line in a file if line number is available

Shell Programming and Scripting
1

Hi guys,
is there are way to substitute the content of certain line in the file by another entry if line number is available?
For example, I have a variable A="HCMLPBBG" and a file MYFILE.
I need to substitute entry on line 18168 of MYFILE with the value of the variable "A".
Is there a way to do it?
Thanks a lot for advice.

2 
awk -v LINE=18168 -v A="$A" '{ if(NR==LINE) $0=A; } 1' < infile > outfile
cat outfile >infile
rm -f outfile