Yes, use the same procedure as the firmware upgrade but select the old version of the FW you wish to use.
If when attempting to revert to a previous version of the firmware you get a message like this: Unable to complete firmware upgrade (error extracting /tmp/….tar, the file "/main/firmware/smith-XXXXX.img" already exists) you will need to delete that previous firmware image file before you can proceed.
You can do that by SSH-ing into the printer and entering this command:
where XXXX is the version number as given in the error message. (You can just copy the complete file name and path out of the error message.) Then perform the downgrade again using the usual procedure for a firmware upgrade.