In your opinion, Is it safe and not too complicated to use a universal kit to hook up a new range?

Also, can the old hookup be used usually, in your opinion?

Thanks in advance.

What is " the old hookup "? The fixed gas line? The flex gas line? Flex Gas piping is flare fitted. When you remove the female end and put it back on a different end, it may not properly seal or may have been distorted using a wrong wrench. You should always use a new flex line when connecting anew appliance. If I am not mistaken, If you buy a new gas dryer from Lowe's or HD and have it installed by them, they will require a new flex line..