Can An Exclusively Breastfed Baby Have The Occasional Formula Bottle?

My mom wants to be able to give my baby formula bottle when I’m not there. Can this be done? He is exclusively BF, 4 months old..

How Do You Start Formula For A Breastfed Baby.?

I am going back to work and I want to start giving my baby formula in addition to breast milk. I am interested to know how others started their breastfed babies on formula. She does drink from a bottle.
I don’t want to completely cut out breast milk. I just want to add formula in. Tell me about your experiences and ideas on how to make this convenient for my baby and me!