
I think it is enabled by default.How is the A9LH overwrite protection enabled, I dont remember seeing an option for it.
Is it already enable if I followed the full guide.

The latest version does not have the option to disable any of the patches that Luma adds, at least not from what I can tell. I haven't used older version to know if that was even an option.I think it is enabled by default.
You can go into a configuration menu by holding select and turning on your 3ds.
Somewhere around there you will see that option, but the name may be a little different.
PS: I think in the newest versions it is always enabled, so you're good to go.
The latest version does not have the option to disable any of the patches that Luma adds, at least not from what I can tell. I haven't used older version to know if that was even an option.
So long story short FIRM protection is on by default and I don't think there is a way to disable it.