How to jumper to a new electrical main while the old service is still being used and transition over slowly?

don't really understand what you mean?

if you have a 60 amp service and want to change to a 200 amp svc.what are you running off the 60amp svc.? my cond.unit runs off that. the only way you can change is to either do one run at a time or do it all and you at once but either way your going to have to break the service while you are doing the change over.don't think there is an slow change when it comes to redi kill a watt. and your going to have to have it inspected by the city or co. before the pwr.co. will hook up the meter. and it has to be up to code before they will inspect it.

don't forget about those nasty old permits you have to pull.

Your explaination is confusing..!!>.. but if the power company is going to change the main wire coming in just change out the breaker as he turns off the power so you wont get shocked!

install the box run a 10x3 with a ground to the old box attach the ground and common and attach to a 30 amp double pole breaker,run the wire to the new box attach the black and red wire to the hot block where the new wire will be installed place the white wire on the common and ground to ground.........install what ever breakers and run where you want ,but don't pull more than 30 amps.............tom