Question - once I created a data source, can I add dimensions and/or measures off new fields without re-creating the data source?

Answer -

Yes.  Select the data source, right click the data source drop down (above the Data Browser) and click Edit Metadata  This feature is a little hidden so we will make it more obvious soon.

However, I do not see where you can change the field type (text, numeric, date).  You can change the field types when you create the data source but how can the field types be modified or corrected later without recreating the data source from scratch?

The short answer is yes, it depends on the type of data source you've created.

1. If you're working with an ElastiCube data source (always recommend) - you just need to change the type in the ElastiCube Project Manager and re-build the ElastiCube.

2. If you're working with a data source created directly over SQL, MySQL or Oracle, you cannot change the type of an existing dimension but you can add it again with the new type by navigating to Data->Edit Data Source Schema.  The old dimension will appear in red as missing and the new dimension should appear in green.  Please note that widgets bound to the old dimensions need to be bound to the new one after this process.