The features you need are COMBINE (page 320 Manual) and COPY(page 315 Manual)
COMBINEMake sure the desired multisample is combined into the same group by hitting the preset edit button
Then hit F2 (Sample Zone) followed by F5 (Combine)
Now when you select the copy command the whole multisample range is copied to the destination preset
COPY (Adding the multisamples to the destination preset)
While in preset edit mode Select the preset you wish to copy
Highlight G1(Group 1)
Hit F1 (Utilities)
Hit F4 (Copy) and place source preset into destination preset
Change the group number of the newly added multisample set to group 2
By changing the group number you can now individually alter pan, volume, transpose chorus, slide filter etc of either multisample set.
Then just
export the newly created preset and this will save only the needed samples from the samplers current memory, and it will ignore ones not used in the preset
This took me a while to learn, I hope it helps