Hi, I literally just had this problem happen to me (bootrom error) on a n3dsxl. Hope this isn't out of line to ask but is a hardmod my only option? I have my NAND backed up, got to part 5 step 29 of the a9lh guide. It installed the NAND fine, went thru stage 3 then the error occurred. If hard mod is the only option can I still install one and where's a good place to get parts? Thanks for your time!
https://gbatemp.net/threads/tips-and-tricks-for-hardmodding-a-3ds.418402/