I have an old CEB 100 AMP panel and I want to replace it with a new Square D 100 AMP panel that has more spaces/circuits. I have 2 problems. The #2 alluminum feeds coming from my meter base are not long enough and a set of #6 copper lines running to a sub panel in my shop are not long enough. Can I use a junction box and some type of connectors to extend both of these lines? Both lines are in EMT.

If you are changing out the panel, you will need to get a permit and an inspection. The power company may require the inspection before they are willing to reconnect their equipment.

Also, you will need the power company's permission to pull the meter. Normally (at least in this area) they will let licensed electricians pull the meter, but not home owners, without proof that the homeowner knows what they are doing. Trying to move a live circuit can get you dead very quickly.

My immediate suggestion is, once you get the power off, place a main disconnect switch at the location where the service cable enters the home. Ground and bond the switch to the existing system for the panel, then remove the panel's grounding and bonding connections. Now call for the inspection and get the power turned back on.

Once the power is back on, you can replace the main panel by operating the disconnect switch. Now replace the panel, but do not bond ground and neutral together in this panel. It is now treated as a sub-panel. With the new panel installed, make sure that the Main Breaker is in the open position (just for safety) and that the main bonding jumper is not installed.

Run 4 wire cable from the output of the main disconnect switch to the new panel. Reinstall the breakers and branch circuits.

Have the work inspected and then you can return to the main disconnect switch, and close the switch, then close the main breaker if that is required.

Trust me, you do not want to do this work without inspections to prove the work was completed properly.