i think i might have something that works here...

_base.py

@@ -60,8 +60,8 @@ class BaseUpdater(object):
                      self.old_hash)):
             self.do_update = True
             self.download()
-            if self.do_grub:
-                self.grub()
+        if self.do_grub:
+            self.grub()
         self.touchVer()
         self.unlock()
         return(None)

tpl/sysresccd_grub.conf.j2

@@ -17,8 +17,7 @@ submenu 'System Rescue CD' {
 		insmod loopback
 		search --no-floppy --fs-uuid {{ disk_uuid }} --set=root
 		set isofile='{{ iso_path }}'
-		probe -u ${root} --set=imgdevuuid
-		set imgdevpath="/dev/disk/by-uuid/${imgdevuuid}"
+		set imgdevpath="/dev/disk/by-uuid/{{ disk_uuid }}"
 		loopback loop (${root})/${isofile}
 		linux (loop)/sysresccd/boot/x86_64/vmlinuz archisobasedir=sysresccd img_dev=${imgdevpath} img_loop=${isofile} earlymodules=loop
 		initrd (loop)/sysresccd/boot/intel_ucode.img (loop)/sysresccd/boot/amd_ucode.img (loop)/sysresccd/boot/x86_64/sysresccd.img