At the time of writing yes.
BUT if nintendo pushed an update that forced 11.0 FIRM to be used, then it would break our current hardmod hack to software downgrade. If that were the case then the only way to go back down would be to already have a NAND dump of a previous firmware, at least until a new exploit be found; either a new ARM9 exploit or a new way to exploit the NAND dump from hardmod.
If you have a backup of any sysnand / emunand yes.
If Nintendo were to patch arm9loaderhax and you update, thus overwriting arm9loaderhax, you could restore a previous nand dump and be right back in business.
If you have arm9loaderhax and BSOD while using godmode9, hardmod will fix it as arm9 won't have access to NAND.
Long story short, hardmod = direct read and write access to NAND. That's why it's stated to always make a backup of either 9.2 sysnand or whatever the latest firm you have installed with arm9loaderhax.
And if 11.0 get's patched via a native firm update, than that is all that could kill it currently.
Poorly worded title but I think I know what you mean, "Will a hardmod allow my 3ds to be permanently warez hacked?"
If you have made a backup of an exploitable firmware (<=11.0 presently), yes.
If a future firm update comes out and doesn't either have a downgrade vuln or an arm9 exploit, then no if you haven't backed up a firm before that.