I am unfamiliar with Partition Magic so I can't say for sure but in general (of course nothing is absolute) you can use another boot loader. They usually require you to install LILO to the root directory of the partition you want to boot. When you boot with "bootloader abc123" it will give you an OS selection menu. By choosing a Linux OS the bootmanager simply points to that partition and LILO takes over from there so you don't really ever get rid of LILO it just isn't your boot manager. I see no reason that Bootmagic wouldn't work unless it doesn't support Linux filesystems but I highly doubt that.