18 g to 20g nose ring?? Can you stretch it🤷🏼‍♀️

I got my nose pierced a few days ago and while I’m not changing it for a good while I was looking online at jewelry because for some reason everywhere has good sales right now and I would like to purchase some for when I can change it just to have it, but I was pierced with an 18g stud. Online in the stores I’m looking at have a limited selection of 18g jewelry, most of the jewelry I really like and can find more of are 20g studs or hoops. When my nose is healed well would I be able to stretch it to fit 20g jewelry. I was also reading that’s the most common gage used for nose piercings and I can see as most of the jewelry I’m seeing is 20g. Would I be able to go back down to an 18g is I wished. And would it cause any damage or insane amount of pain to stretch it to a 20g? Again I’m not planning to do this for a while but I want to buy some jewelry for my nose while they are on sale and would like to know if I can stretch the hole or not. Also where do you get your jewelry from?