Changing Location ID name in SAP BI routine

Hi

I've requirement where two columns Location ID  - ( having assigned 1,2,3 coming from source system) and job type 0 and 1.

Now In Location ID column I've to assign location A to 1, B to 2 AND C to 3

In job type columns

0 to D

and 1 to N

Please can you example code how I can do in routine... should it be done in start/end or field level routine---

Pleaase give example code.

Thanks,

P