My knee jerk reaction is to say "Deploy your packages". Just create a dev folder on your SSIS server and plop them in there. Its pretty easy to deploy 100s of packages using the deployment utility.

Any reason I can think of to not deploy them and run in design mode in BIDS is negated by your volume of packages.

even so... Running in design mode mimics runtime, so if you are in BIDS, you can see that your Connection is pointed @ Server ABC and you know that your package config is set to server XYZ, then wen you click Run in BIDS, Pre-Execution will go pick up the value from your config table and use it.

What I'm not sure about tho is, since you are running in design mode, if you DSTX that is open in BIDS gets overwritten with the config table values. So in the case of the above example, after completion is your packakge that you have open in BIDS showing server XYZ, or is it still ABC?

I can't remember.

If the above doesn't mae sense or does't work out... you can put your 100+ DSTX files in a folder and user a text editing tool do a masive Find/Replace on server ABC changing it to XYZ, then open each of those DSTXs and run as you normally do.. But I advise against tinkering w/ DSTX directly.