Not directly, but you can downgrade 11.0.33 X currently with two methods.
1) A 3DS running custom firmware that can buy a copy of Fieldrunners/Legend of Exidia. We inject a save file into the DSiWare, and system transfer to the stock 3DS. It works, but is time consuming and really annoying. It basically rewrites the section of code that "hard codes" titles in 11.0.33 and gives you a frankenfirmware. Not bad, but takes forever, and if you system transfer back to the original 3DS, you have to call Nintendo to unlink the NNID from the downgraded 3DS. And then you have to use the usual method of PlaiSysUpdater to downgrade the system.
Pros Easy enough to do. Can dump the firmware before you downgrade.
Cons Need to call Nintendo to unlink the 3DS NNID (if you want to continue using that NNID and Fieldrunners - I've been using a burner one, and restoring my no NNID system backup), has a seven day cool down due to the use of system transfer, need to buy an actual eshop game (if you don't have a credit card OR funds needed), needs another CFW 3DS.
2) Hard mod. Four really tiny points on the 3DS motherboard, and requires really specific hardware to do. And a ton of experience with micro soldering. Same idea, but you are directly rewriting the chip with the old 10.4 NFIRM code.
Pros Really fast to downgrade, and you can dump the NAND chip just in case. No 7 day waiting period in between the systems.
Cons Needs a ton of experience to do. Needs a ton of equipment to do (soldering wire, flux, thin wires, usb reader, micro SD to SD adapter, soldering stand).