I have not met nor worked with many Honda trained mechanics that knew or followed the correct bleeding procedure on these bikes but I have assisted members who've wanted their systems bled correctly after their trustworthy Honda trained mechanic worked on their bike
While you can move fluid from either system, you will not be able to purge the air out of the system correctly unless you do the entire procedure from start to finish.
Optional antilock brakes (ABS) and traction control system (TCS). 1996 and later Models equipped with ABS also have front-rear linked brakes (LBS).Haven't seen this point specifically addressed, but the reason you don't want to bleed "just" the rear brake is because the the brakes on an ST are part of a linked brake system (aka combined brake system). The rear brake is not an independent unit. The article that Mellow pointed you to has a nice colored chart in a post on the second page showing the system. Hit THIS link to go directly to that post. Just click on the colored charts to expand.
A bit more technical explanation of the Linked/Combined brake system can be found on the Honda website HERE.
Thanks for pointing this out Topgun. I had flat forgotten that LBS was a feature of just those post '95 models that came with ABS. I should have remembered since my first ST1100 was a '97 standard non-ABS. My other 2 were ABS models.Optional antilock brakes (ABS) and traction control system (TCS). 1996 and later Models equipped with ABS also have front-rear linked brakes (LBS).
ABS model years from 1992 through 1995 have traditional separate front and rear braking systems.