Like to know the easy way to disable LCR and make the system a simple KEY system behind centrex Dial'9'

This is fairly straight-forward - just make line buttons on phones. Press the line key to draw dialtone from CO then dial 9 to get past the centrex.
You may need to disable "LCR Out only" (or some similar). And your traffic reports will be skewed.
Pay attention if you have analog stations or voicemail outdialing - as they may be adversely effected by the change.

If you disable you can just reprogram the keys for trunk groups instead of a LCR key. And yes if you are using out in voice mail or single line sets you will need to check dialing out on them after.

Thank you for your input. I just activated Alternate Dial Plan and then set lines to type 012 and then set ext's to dial out using 300-001 key programming for trk grp 1. That worked perfectly.

P.S. Most all of the phones were single line.

I have to chuckle... in first post you ask about operating as a key system then in last post you mention that most phones are single line. By classic definition, those two are incompatible. Glad you worked it out.
Cheers!