Hi @
xgarb,
You do not need to change prepareCndSubstring() method in this case at all. You should define a new condition in your ItemsList, e.g. TagsSubstring and then add the handler of this condition to \XLite\Model\Repo\Product class.
See more about conditions here:
https://devs.x-cart.com/getting_started/working-with-database.html#method-search
See example of adding such condition to ItemsList here:
https://devs.x-cart.com/basics/itemslist_in_admin_area/
see how we define getSearchCondition() method there.
Please, let me know if it makes sense to you.
If it is unclear what I am trying to explain, please let me know. I will be happy to help.
Tony