Heres what I did.

1. Load the plugin OrbOfDivines.esp in xEdit.
2. Expand the Dialogue Topics category by clicking on the [+] next to it. This will give you a whole crap load of records, each with a little expandable [+] signs next to them. You can totally ignore everything else such as Dialogue Branch, Dialogue View, and Quest.
3 Scroll down the list of Dialogue Topic records until you find the romance related ones. These are all things that you as the player character can say to Lyssia. These begin with the record shown as:
[+] 04DA8521 ASESayOnceRomanceBTopic Lyssia, I've been thinking...Where do you see your future?
4. Expand that record and it will show a sub-record. This sub record is Lyssia's response or chain of responses to the previous dialogue from the player. There may be multiple, even many, such sub-records for any single dialogue record, each with it's own unique conditions or combinations of conditions that determine which response is given (such as one for if you're married and another for if you're single). The sub-record you should see here is shown as:
04DA8534 Ah, Guardian, forever the inquisitor. My future, you ask?
5. Click on this sub-record to open/view it's contents on the right side of the xEdit window. Scroll to the very bottom of the records contents. You will see a section labeled Conditions with seven Conditions listed below it, which will be:
[-] Conditions
[+] Condition #0 Subject.GetInWorldspace(EldergleamSanctuaryWorld "Eldergleam Sanctuary" [WRLD:0003A9D6]) <> 1.000000 AND
[+] Condition #1 Subject.IsInInterior <> 1.000000 AND
[+] Condition #2 Subject.HasAssociationTypeAny(Spouse [ASTP:000142CA]) = 0.000000 AND
And it keeps going from there all the way to Condition #7.
6. Right click on Condition #2 and select Remove (or just click on it and hit delete button). That's it. You have removed the relevant condition form that particular set of romance related dialogue and she will now engage in this dialogue with you regardless of your marriage status with anyone else whereas before she would not have spoken to you about this if you were married. Now you need to do the same thing in the next 10 romance related records in the list. These begin at 04DA8535 ASESayOnceRomanceBTopic1 and continue to 04DA8549 ASESayOnceRomWaitTopic. Each of those records has a single sub-record with Lyssia's responses and those sub-records all have the Subject.HasAssociationTypeAny(Spouse [ASTP:000142CA]) = 0.000000 AND condition in their list of conditions. Dlete/remove this condition from all of these lists.

Congratulations, now Lyssia never checks on your characters marriage status and you can pursue her romance quest quest and dialogues even if you already have a spouse. Lyssia has many more romance dialogue after this but none of it has any such conditions until you reach her marriage related dialogue, at which point she starts checking on the actual vanilla married faction (Target.GetInFaction(PlayerMarriedFaction [FACT:000C6472]) = 0.000000 AND). In the LyssiaCompletelyMarriageBlind patch I removed this condition as well so you should be able to initiate her marriage related dialogue even if you already have a vinalla spouse. However, I don't know how this will play out with the vanilla marriage quest (Bonds of Matrimony) and the Temple of Mara ceremony. It will almost certainly dead end with you unable to continue after her accepting your proposal unless you reset those quests and possibly even remove yourself from the married faction for the ceremony to complete and her become your new wife.

Oncee that's done you should be automatically put back into the married faction again along with your new spouse, but I don't know how the your previous spouse will behave/treat you from then on. Best case is they might still speak to you as of you're married and just no longer have the unique spouse functions and dialogue (cooking you meals, opening a store and giving you a share of the money, Hearthfire DLC function to assign them to your player home, etc) as the game only recognizes your new spouse as being your spouse. Worst case I imagine is that your previous spouse either goes back to just being a follower and treats you as of you were never married or if they have custom "break up" dialogue they might treat you/speak to you with hostility as if you cheated on them