You might run into a couple issues if you continue:
vbelloir wrote:I use Windows on dual boot, to get more efficiency. But sometime, I need to run it only few minutes, so, instead of reboot, I prefer launch the VM.
This will result in changing 'hardware' in the OS, from physical to virtual and back, with Microsoft's activation servers hiccuping over each change. Eventually, you might not be allowed to change anymore. See
viewtopic.php?f=7&t=98410 for a possible method.
vbelloir wrote:I run some software that can't be run on wine : Altium Designer
If your programs need good graphics, you probably won't get as good or good enough in the VM as in physical boot. VirtualBox is not designed for graphics-intensive apps.
Your physical drive appears to already have a Linux partition on it. Was it a dual-boot setup, with grub controlling boot to Windows or Linux? Further editing grub might bung up the exiting setup. (I don't really know, though, I am a Windows guy). I'd recommend good restorable backups of both the host and the external drives, lest that 'data loss' warning bite harder than expected.
vbelloir wrote:setting with Grub...in the VM, on in my Linux Host
If the edit is for getting the VM to boot to the correct partition, then in the VM, definitely. "What happens in the VM stays in the VM." Edits to the host grub would not affect the VM, since the host OS is not running yet, so the VM would not be running yet either. On the other hand, editing the VM's grub to boot to Windows in the VM might upset booting physically. I bring to mind the bite of 'data loss' mentioned earlier.
A Stack-Exchange-style "frame challenge": Can you transfer to a separate VM the things you need to access for a few minutes and leave your physical-boot Windows unchanged? Or are you trying to access Altium Designer briefly during the short VM boots?