Re-open Fixed Asset Year to un-do disposal (unofficial steps)

1.  Run a Select * from FA40200 and note the CURRFISCALYR of the books.
2.  From SQL studio, update the FA40200 table and set the CURRFISCALYR to the year that the asset was retired in.
3.  Go back into GP and undo the retirement.  Interface the transactions to the GL and delete or post them as necessary. 
4.  Go back to SQL studio and update the FA40200 to set the CURRFISCALYR to what is was before you updated it the first time.
Voila.