Dear Indranil Sen,
As per my knowledge it is not possible to mention more than 6 source and target fields for a derivation rule.
Because for that program, SAP defines that (1+5) fields for that screen.
That is the reason you are getting the gray color after 6 entries
Yes we can increase that limit but for that we need the access key.
If you have access key authorization, you can increase the limit
Reasons in details:
Screen filed what you are looking for is:
DYNP5400-SRC-NAME-FIELDNAME
There you can enter (1+5) entries only. enhancement for that field is difficult.
So you can opt for 2nd option as you said.
Let see Mr. Waman Shirwaicar's views on this issue.
Regards,
Pavan Kumar Arvapally