VERIFIED SOLUTION i

MailStream Plus 8.3.0- Resolving Why did postage go up (or down) due to Standard Mail Flats now getting FSS rates? And is FSS preparation required? How about for CRRT HD and HDP mail?

Prior to May 31, 2015, the USPS had no actual FSS rates for mail pieces.  Although they were prepared in FSS bundles per the USPS regulations, they got the same rate that they would have got had they been prepared in Carrier Route (CRRT) bundles, 5-digit bundles, etc.

Beginning on May 31 (i.e. with MailStream Plus 8.3.0)  pieces going into FSS bundles now get FSS rates.  So mailers  will see a change in postage due to that.  
Pieces that were getting CRRT rates before will now pay a higher rate per piece under FSS.  Pieces that were 5-digit before now pay a lower rate under FSS, etc. 

Per the USPS, FSS preparation is always *required* for Standard Mail Flats pieces with ZIP Codes specified on Labeling List L006 column A.  The two exceptions are:
1)
Carrier Route Walk-Sequence Saturation pieces are never included in FSS.
2)
Carrier Route Walk-Sequence High Density (HD) and High Density Plus (HDP) can be excluded from FSS at the mailers option. The High Density and High Density Plus rates are currently lower than FSS (as-of May 31 2015 prices).  
Whether to include them in FSS is controlled in MailStream Plus via the ALG BL parameter position 26.  The default is yes, to include them in the higher rate FSS.  But you can select to exclude HD, or HDP, or both.
UPDATED:  April 14, 2017