Prefix a tag to a record in a flat file and then send to process

Hi,

I have a flat file having Batch Orders.

Flat file:

Order1
Order2
Order3 and so on.

where an order consists of

00Headerdetails
05parentdetails
10child1details
20productA1details
20productA2details
10child2details
20productB1details
20productB2details
99Trailerdetails

or

00Headerdetails
10childdetails
20productA1details
20productA2details
99Trailerdetails

The tag Identifier for Order is '00'. And all Header, Parent, Child, Product records are positional. Only Parent Record is optional.
Due to some constraints (for invalid orders if an inbetween data has 00, BizTalk assumes that as an Order and tries to validate causing a havoc in the event entry log)
So I think i would try a 2 stage approach.

Stage1: prefix "PO:" to every Order in the input flat file(Irrespective of valid or invalid),so that I get an output flat file. 

PO:Order1
PO:Order2
…
PO:OrderN

Stage2: Use debatching and my new schema is more strict and Tag identifier as "PO:". So then I could validate and seperate the invalid Orders.

Problem I am facing:

To prefix "PO:" I am using BizTalk. Input and Output schemas are similar (but want to add an extra field to get the "PO:" value). and use a map.
 Because I want to pass all orders whether valid or invalid, I am finding a problem. I have defined all the records in the schemas – min occurs = 0;
 but this gets me into further problems.

Please can anyone help me out here. Or atleast tell me how could i prefix PO to each Order, whether valid or invalid( the only clue I think is using 00 which is the first 2 positions of the order).

Thanks in advance.