No this is unwise and you are over thinking it. Do not create any digital footprint relating to your specific project details (like a fake posting), and lying about being craigslist scammed will just result in them not finding any relevant craigslist posting if you don't make one, that is if they were to investigate. Chances are they wouldn't give a shit how or why you got there, just that you are there.
The following is for the most part illegal activity/advice, be smart. This is advice for a potentially successful long term hostile takeover. If this were just some bando, I would say just walk inside.
Your best bet is to gain entry through a window or a door, this may involve damaging something that needs to be replaced. This period is critical between gaining entry, masking/repairing your entry, and changing ALL the exterior locks. This could be the difference between breaking and entering/burglary/prowling and trespass/criminal trespass or vice versa, or whatever relevant criminal codes apply in your jurisdiction.
Another thing to consider, like any good burglar would, is there an active alarm system. Even though the property is vacant and foreclosed, the bank or creditors still sometimes don't mind paying the extra bucks to continue the use of one of these. Easy way to find out? Go at night, sometime relatively early after dark, not early AM, and stealthily see if you can open a window (like a rear or side one). If you are able to open the window (or door), open it to its maximum range to trip any sensor, wait 30 seconds, close it, and walk away. Find a reason to be down the street, walking a dog is good, see if the police come by. Chances are there isn't an alarm, but you never know. If there is, find a new project.
If you can't force a window, you may have to get dirty and physically get inside (prying a door, breaking a window, drywall tunnel, etc.). If you are faint of heart and a law abiding citizen I would not recommend this. This is indefensibly a burglary if you are caught before you can clean up your mess.
There are all types of other home defense alarms, the chances of encountering an active one in a long vacant house are slim, but it is possible. There are also sometime fires alarms interconnected with these, don't fuck with smoke detectors if there is a integrated fire alarm system (often times a massive wall mounted red box in the basement/utility area, usually in larger buildings)
When I decided it was safe to enter (probably another evening) I would go in at night (through your tester spot if applicable) and sleep on the floor out of view (closet?) until the following morning (on a weekday), having everything I needed to change the locks and mask my entry point if need be with me. Don't do anything overnight, no lights. I would set to work like any worker would sometime after 9AM (it is LA, so maybe 11) and clean up any mess I made getting in, do any repairs, and change and test all the locks, and lock ALL the windows. Then I would casually leave and return at a later date.
Once you possess keys I would start showing up at random times and just going inside, and waiting, observing the outside. Even if people see you going in, they are too concerned with their lives, maybe you're a realtor, or a worker. It's not that serious. Don't act like you're doing anything you shouldn't be and people tend not to think you are. Do this at normal business hours.
After that I would assess the situation on a case by case basis of how much I really wanted to settle into this location. Do not run if you happen to encounter someone attempting to gain entry when you are inside, you'll only arouse more suspicion. I would be especially sketched about driving or leaving any vehicle connected back to me here or near here as well AT ANY TIME. Another thing to think about is don't dress like you are on tour with Left Over Crack when conducting any clandestine operations.
If you are to encounter anyone once you've gotten control of the building, it's up to you to see what you could pull off telling them. I personally like reversing the script and asking what they think they are doing there. There are all sorts of things you could say depending who shows up. The police legally can't force their way into the building, that doesn't mean they won't, they're just not supposed to. So don't answer the door if they arrive at some point. Encountering anyone before successfully gaining control looks pretty bad and chances are you're up shits creek and probably should move on.
If you chose to move in and actually dwell here and someone comes to tell you to get out. Tell them it is your house and you live here, you have keys, and hopefully at this point, other things tying you to the house. You do not legally have to disclose who your landlord is or how you got possession of the house. The police, if involved, will try and tell you that you have to, and blah blah blah, and maybe even force you. Keep reminding them that this is a civil matter, whoever wants you out has no paperwork with your name on it saying you are a tenant, and therefore you must be removed by a judge. It is very easy to cave to police pressure. But if everything goes good, you'll eventually be summoned to civil court, to prove it's your house. Postpone this and drag it out. Hopefully none of that will apply to you and you can live there without having to deal with that.
Bring others in to live with you too, power in numbers, free housing for everyone. End homelessness, wrench the system.