replaced the build.prop file with twrp but changes are not applied? plz help

[Android Central Question]

i decreased my dpi of rooted lg v10 to 540 with texdroider app after reboot it was applied but system ui has stopped error dialogue box appeared which didnt allow me to even switch off my phone bcz when i click ok then it appears again so i went to my twrp and coppied build.prop file to sd card then i edited the dpi in it to stock value which is 640 with notepad++ and copied this edited file to sd card and inserted it into phone and again i went to system folder with twrp and deleted the build.prop file from it and copied the edited file which was on sd card but the problem is that system ui has stopped error is still coming after reboot and dpi also seems same as 540 then i copied the build.prop file again in sd card and opend it with notepad++ and dpi is showing 640 its mean that build file has been edited correctly but changes are not applied so what would i do to the them plz help me i m sooo confused.