They won't need to be restrung so often if they are not worn.
It's time to restring if ...
• there are unsightly gaps between the pearls, caused by the silk thread stretching, thanks to gravity!
• the silk appears grimy. Silk absorbs skin oils, lotions, sweat, environmental pollution etc. This weakens it, besides dirty knots not looking nice.
Pearls are soft and should be stored apart from other jewelry that may scratch them. In a soft cloth bag, for example. They should not be kept in a plastic bag as they need moisture from the air. Also do not keep them long term in a safe or safety deposit box, for the same reason. If you do store them in a safe, place a small dish of water in there, too, to add moisture to the air.
Wearing the pearls occasionally is good for them as they will absorb moisture from the skin. Pearls shoud be the last thing put on and the first thing taken off. When they are removed they should be wiped clean with a soft cloth. I like microfiber for this but any soft cloth will do.
As for restringing, you can probably ask your local jeweler about this. Many jewelers have someone they send their pearls to for restringing. The cost may be $3/ inch or more. You can also send them out to be restrung yourself. Pearl Paradise, for example, offers restringing service. Link:
https://www.pearlparadise.com/produ...paradise-com-item?_pos=2&_sid=27ac3d0b2&_ss=r
However, many of us restring our own pearls; I do. You can see tutorials on the Lowly Beaders Club forum. It's not hard and it definitely saves money, and then one can modify the necklace as desired.