Large sms thread in HideSMS

[SweetSaudade]

I've been using KeepSMS (an app that hides texts and requires a pin to access it and doesn't appear on the recent apps list, etc. Many use it to text secretly but I've been using it to avoid the thread limit of 5000 on the stock sms app). I neglected to consider that I may need to back them up at some point.. Now I want to do a factory reset but I have no clue how to back them up first (KeepSMS does not have any ability to backup/restore, I checked), and I need to save them. I can unhide them in order to use SMS Backup and Restore, but what will happen to the ones that are over 5000 messages in length? One thread is almost 20,000 messages - will the stock app delete them or will they be in groups of 5000? I have been searching for hours online trying to figure out what the file might be called where these msgs are saved so I can just copy that folder to my SD card but I am only finding info on the KeepSafe app (for hiding pictures).

(sorry I continually confuse the name for this - it is listed in the play store as Hide SMS but on my phone it has the name KeepSMS)

Really hope someone can help.. Thanks!