Allow me to try a comprehensive explanation of why that won't work.
The boot sequence is: Power on > Bootrom (> ARM9Loader, New3DS only) > NATIVE_FIRM.
OTP is locked by setting the CFG_SYSPROT9 bit (which can only be unset by a hardware reboot). Once this bit is set, reading the OTP will give you zeroes.
On O3DS, this bit is set at the beggining of the ARM9 binary in the NATIVE_FIRM. <2.1 NATIVE_FIRM are not setting the CFG_SYSPROT9 bit.
On N3DS, it is set by the ARM9 Loader, which is a normal firm viewed from the bootrom (only doing some checks before decrypting and giving code execution to the real firmware). It always sets the CFG_SYSPROT9 bit.
A9LH is exploiting bad checks in the ARM9 Loader (= only exists for >8.1 firms). But too bad, it is triggered AFTER the CFG_SYSPROT9 bit is set. We have the same problem as with the suggestions of 2.1 emuNAND, once locked, that's over. Loading a 2.1 FIRM from A9LH serves no purpose (and will certainly won't work without many changes).
What Sumea said is very true: for now (who knows in the future), OTP is only used for *FIRST INSTALL* A9LH and only work for the console it was dumped from. You might want be sure you want to get that OTP, it has no use for A9LH'd consoles today.