Programming :: Sed To Change Character In Text File Only Once?

I have a script that looks like:

Code:

cat servers.txt
trivia:P:N
trivia:D:N
tucana:P:Y

[code]....

I want to be able to find the lines that matches my input and change the N to a Y, but only for the lines that matches the name and not any other N's My problem is the line does not always contain a P as it can be a D as well so my matching did not work. If my script issues the name $1=triva the lines will change to:

Code:

trivia:P:Y
trivia:D:Y

I have the following code so far but as you can see it does not change the D's

Code:

sed -i 's/trivia:P:Y/trivia:P:N/g' servers.txt

*** UPDATE ***

should I be using a method as follows? I am still stuck on the changing all instances though.

Code:

$1=server
sed -i 's/$server1:P:Y/$server:P:N/g' server.txt
sed -i 's/$server1:D:Y/$server:D:N/g' server.txt