(Your English is excellent and nothing to apologize for.)
I have Slacked since v. 10. I've never seen an option in the installer to skip LILO, but I've never installed for dual boot because I didn't have to.
I did find this LQ thread
. Maybe it will help.
It would be a good idea to back up your grub anyway. There's no such thing as too many backups.
Have fun with Slack, but be careful. Once you Slack, you'll never go back.