Mitsubishi GX Developer - uploading/downloading/ memory plc

[letranlong]

I need to do some research on Mitsubishi PLC program. I want to download original program (made by someone else, I have no source code) and save on PC (with GX developer) from PLC, play a little with its copy (on PLC) and then upload original program to PLC. Is it safe ? Will PLC work as before manipulating program ? Are there any traps ? Is you can guess I'm starting my adventure with this technology
https://www.youtube.com/watch?v=mVz87yf_cyY