Google "RemoteDLL" or any program similar. Program will select the process and then .dll you wish to inject.
Alternatively if using GWCA you can create a .bat file and use any of these methods:
example:
Code:
"C:\Users\WindowsUser\Desktop\GWCA\Release\newloaderv4.1.exe"
--lib "C:\Users\WindowsUser\Desktop\GWCA\Release\Graphics.dll" --wndtitle "Guild Wars"
pause