Transplant/Soil change

So the plants I have, came in a "custom" soil I have no idea what the level's are of it. I also cannot get it easily.

When it comes time to transplant I'll need more soil... Will it hurt my babe's if I switch up to another soil?

Has anyone encountered a problem like this? And what would be my best bet with the new soil I purchase?

EDIT/ Just need to know if there are any special conditions that I have to meet or if I can just got get any type of growing soil...