How can I modify the lem10's system.img?

I was trying to modify lem8’s system.img with a romtool few days ago,and succeeded.

I recently got LEM10, I also tried to modify LEM10’s system.img with the same ROMTOOL, but any attempt failed, the modified img file SP into LEM10 will cause it to gets stuck in the booting interface(Any changes to system.img will cause this to happen). I want to know where the problem is?
What software do you use to modify the img file?THX!

dont know but look for Hovatek videos