Hi!
Bonding rules apply as normal, but there is a chapter on special aspects in our comprehensive bonding guide.
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
Please be aware that any cross gender bonding stands and falls whether initial acceptance happens and whether a hierarchy can be established in the days following the bonding. You can interrupt a bonding that is heading in the wrong direction and resume on another day, but you have to be aware that once piggies have made up their mind that they dislike another, they are not going to change their mind; not in years to come! Give any bond plenty of time in the bonding pen; if necessary several days until you are sure that they have settled together and are fine.
In my own experience many cross gender bondings fail at one of these initial hurdles; especially with adult and even more so with older sows. Young sows at ideal pup bearing age will be pushed by their body chemistry to accept a boar and most of those bondings work out.
There is however never a guarantee that a bonding at home will work out; it all depends on whether the personalities mesh and whether a new addition is welcome or not. Ideally we recommend to rescue date for that reason. Please make sure that you have a plan B before you start in case you end with a grudge match. You can give your piggies the best chance you can provide, but it is between them whether they want to live together or not, and there is nothing you can do to change their personality and the dynamics between them when the chips are down. Piggies are every bit as complex as humans when it comes to relationships and arranged marriages...
All the best!