Using an External Filter to modify a existing column

[GSIDSXGrp]

I've a row that contains a id column, storehours and a series of open/close times for each day of the week:
ID StoreHours OpenMon CloseMon OpenTue CloseTue OpenWed CloseWed ...
1 NEED_TEXT 09:00 21:00 09:00 21:00 09:00 21:00
2 NEED_TEXT ...

Passing this row into a External Filter I need to change NEED_TEXT into a pretty formatted string like "9:00 am - 9:00 pm Mon-Wed<br>".

I've the code that converts the times and creates the string however when I view the results using a Peek Stage only the first "9:00" is displayed. From what I've determined this is caused by the field delimiter being a space character.

Is there a way to change the field separator? Or am I abusing the External Filter stage and should use a different stage?

One thought was convert the data into an XML chunk, passing to the External Filter, than converting back to tabular.