Dev1 --> Dev2 --> Live
I have a few new custom fields to deploy in the live system
It was created in Dev1 and added as a changeset (validated and deployed) to Dev2 (for testing) As there were no problems we want to upload the same changeset to Live. How can I do this instead of creating another changeset from Dev2 to Live?
If you want to use change sets from Dev2 -> Prod you will have to create a new one in Dev2.
Alternatively you could deploy the changeset directly from Dev1 -> Prod (As long as you didn't make changes in Dev2).
However I would suggest looking into other deployment methods instead of changesets if you will have a multi-environment deployment route. Using the Force.com Migration Tool you can deploy to any environment just with the metadata - think of the local metadata as your changeset, you can then deploy that anywhere (even outside your Production environments).
This is currently not possible using changesets.
There is an idea over on success.salesforce.com which after 6 years has gained enough traction to garner a hand-wavy, non-committal reply around one year ago from Salesforce.
As others have pointed out, you cannot do this using Changesets. You are forced to create another one.
If you are open to other tools that can give you similar (and more) functionality, then take a look at our product, SnapShot (https://appexchange.salesforce.com/listingDetail?listingId=a0N300000016YhyEAE). It has some cool features that you might like.
Sridhar
