UNIX for Dummies Questions & Answers

I have the following sed command:

sed '/7361105/s/^\(................................................................................................. .............................................................................\)....\(.*\)/\16776\2/' arch.txt > arch.tmp && mv arch.tmp arch.txt

and I would like to replace the n "." (174 characters) in the first expression, to an expression that does the same (indicate that I want to replace from character number 175).
I've checked it out in manuals and tutorials but I can't seem to make it work.
Any ideas?

Code:

echo 'qwerty' | sed 's/^\(.\{2\}\)..\(..\)/\112345\2/g'

Does the '2' in the pattern mean the no of characters to make the pattern?

that's correct.

Thank you very much for your help!!! I could make it work just perfect!!!!!