Can't say anything about running the HAAS machine as a HAAS machine as I don't have one to play with... But as for using the HAAS post processor in SolidCAM and thinking that you need to relearn anything is incorrect.
You only need to change posts to get any output from SolidCAM formatted to suit the target machine. How you use SolidCAM is still the same, it is only the selection of the post at the start of the programming process that is different. Select the HAAS post and carry on as per normal.