Hi I'm using a stock LineageOS rom specifically android Pie (LineageOS 16) and I've been modifying system applications, such as SystemUI, framework, gallery, sms etc. before (on samsung ROMS) and so far I haven't got any problem aside from forgetting to set the correct permissions on each apk.
Though when I switched to LineageOS, it seems that I can't simply modify the framework and systemui. I tried the usual way of decompiling and compiling an apk using apktool, then, to sign the apk with its previous/original key, I use the files from the "original" folder in the decompiled apk then build the apk again. Somehow, when I try to replace the apk in my phone, set the correct permissions, and reboot, it will result to bootloop.
Did I miss anything? Do i need to sign it with another key? Do I need to disable signature-check on my Android?