This is not really what you are looking for, but it will allow you to change the path of a block definition in python by putting strings through the Rhino command line.
import rhinoscriptsyntax as rs
for Block in Blocks:
cmd+=Block+" " #Block Name as a String
cmd+="LinkedAndEmbedded " #How you are storing the blocks
cmd+=BlockDest+" " #The new filepath for the block
rs.Command(cmd) #Run string in the Rhino command line
Hope this helps, I attempted to do something similar a while back and I was unable to do everything I needed for block editing within the rhinoscriptsyntax and scriptcontext, so I ended up with this rather unsatisfying solution.