ok so i just finished this tutorial https://www.ultimate-guitar.com/forum/showthread.php?t=1068679&highlight=combo+to+cab and i have a question. if i want to just connect the wires back from my combo to use my combo can i still leave the jack connected to the speaker? without hooking it up to a head of course.
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There are two ways of doing what you want.

Use a switched jack socket for the mod. These are readily available and are obvious by having four solder tags. If you look carefully you will see that when you push a plug in it breaks the contacts between the tags, this leaves two contacts pressing against the plug (and therefore connected) and two now diconnected pins. solder the speaker to the connected pins and the amp output from the combo to the other pins. If you get it right then when you pull out the jack from the head the combo will be reconnected as if you had not done the mod. Incidentally if you wire the socket the other way round you could have a way of using the combo amp to drive an external speaker.

The other way, which is easier to understand and harder to get wrong is to wire a socket to the amp outlet (the red and black wires in the photo) as well as the speaker. Label them clearly! Then you can simply use a short speaker jack lead to connect them together whenever you want. With this set up you can of course use any combination of combo amp/speaker and external amp/speaker so long as impedances match and you don't put a big amp with a low wattage speaker. Have a look at 'matching speakers and amps' in the columnns.