I see in the videos alot that you are converting to poly and then to subd and then back

i have used the script editor and copy the scripts to mel and didnt work that well . have to click on it and sometimes it will work and sometimes it wont if i convert to one and then want to go right back to poly. i didnt know if someone could post a nice script. Cause I remember when you convert back to one you have to keep vertices' poly i think and the other one you wanted to keep something else . is there a toggle script that keeps on the vertices in polys and the other option that is needed to subd

Can you post a nice script or if two are needed ? thanks all.