Move USB installation to new partitions on internal hard drive?

Hi everyone, love Libreelec and very greatful to the people who created and maintained this over the years.

I have what may be a weird request. Currently I'm running Libreelec from a usb thumb drive but was wondering there there would be a way to move that installation to the internal hard drive? I think I have a few ideas how this might work, but I'd like to bounce it off you folks to see if I'm on the right track or wasting my time.

I'm running this on a very old laptop, a 2005 HP DV5000, which was designed for Windows XP Media Center edition. It even came with a little credit card IR remote, so the unit has a built in IR remote receiver. Due to the age I can't run more recent versions of LE but that's not important.

What makes this more interesting is that the laptop is currently set up in a weird triple-boot situation where there are two OS's (XP MCE and AntiX) installed on the hard drive as well as a custom boot entry in my Grub for the LE USB so I can choose it on boot up. I'd like to eliminate the USB drive from the equation.

If I were to shrink the largest partition and use that space to create two new ext4 partitions matching the ones on the USB, copy all the contents from the two partitions from the USB to the matching ones on the hard drive and then reconfigure my grub to reflect the new locations, would that work? Would the kernel get confused and not be able to find the files it's expecting to find?

Am I mad?

Just wanted to update that against all odds (with me being not that bright) I managed to get this to work basically on the first try!

The only real snag I hit is I already had three primary partitions on the drive so what I had to do was shrink the largest one with the most free space down to give me a 15gb unallocated partition. Then I set that up as an extended partition, creating two new partitions inside that for the SYSTEM and STORAGE partitions that EL needs.

After that I rebooted into Antix and had to use gksudo gnome-disks to allow me to mount them and copy the files into each directory from my USB drive. Then using Grub Customizer I copied the entry for my USB drive and edited it to reflect the new location on Disk 0, Partition 5 and save.

Rebooted and it showed up on the Grub and booted up exactly how I hoped.

So, yay me.