If you'll do a Google search for "Non Affiliate Scan on Motorola Radio" or something similar and you'll find pages & pages of results. But I agree, if you have to ask the questions that you did which are basic knowledge when it comes to this then I would do a lot of studying before even beginning to attempt this.
People do it successfully all the time. However, as someone who is a daily user of a P25 public safety system I tend to shudder when it's asked or mentioned when someone asks basic questions that someone that is remotely familiar with Motorola radios would know. Until you've done a lot more studying on it I wouldn't even remotely attempt it. Especially when there are units such as the Unication G4 & G5 on the market, along with the new Uniden SDS100 that is soon to be released. There are a number of system managers out there that watch their systems like a hawk & if they see a rouge ID pop up by someone not authorized, i.e. someone attempting to program a unit for Non Affiliate Scan, they'll inhibit in a heart beat. And often these days they are more apt to prosecute someone for it.
Understand I'm not trying to sound like the SARP, just wanted to offer some encouragement to build your knowledge base, stay out of trouble, and ensure the safety of those who are authorized users of whatever system(s) you're trying to monitor.