Cost Manipulation

Is the following doable? is there a flaw in my plan? Is there a simpler way?
We're 405 CD on V5R1

My boss wants a new cost set copied from standard, except actual cost used on certain combination of item classes of raw materials (this is to be the basis of standard cost for next fiscal year) ... after I do this, he will have a few of the results adjusted slightly before we switch to this for next year standard costs.

My tentative approach plan:
* create logical file join-CJ1
** CMF cost master, only cost set-1 actual, joined to IIM item master, only items of those raw classes that he wants to have actual used in the new cost set
* create logical file join-CJ2
** CMF only cost set-2 standard with IIM all other items (than those in join CJ1)
* in theory all items should be in join CJ1 or CJ2 except any that lack standard or actual cost
** before starting, I could identify any such null situations via no-match vs. active records, then zero such items for safety
* create cost set 13 of CMF to start off devoid of records
* create temporary work copy of CMF as CMF13W identical physical file structure, to start off devoid of any records
* copy file CMF all physical records of join -CJ2 to the temporary file copy CMF13W
* copy file CMF all physical records of jokn-CJ1 to be appended to CMF13W
* use SQL/400 or other tool to replace contents of cost set in CMF13W with value 13
* copy all records of CMF13W appended to CMF
* do a cost rollup of new cost set 13
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Al Mac ... who has not done this kind of manipulation in a while