Permission of Program installed

when i am login as a limited users account, i am not able to close those process which username is “System” in task manager, but i could close it if i login as an Administrator account. My question is:

1) i have develop a program in c# with .exe extension, how can i set the username to ” System” when i running this program or is there other way to change the process username before running my program. My purpose is dunno allow limited users account close this program. how can i do this?