We know that customized field has a limitation of 40 characters in Test Director. Unfortunately my customized field in the Requirements tab, should accept a string 70 characters (maximum) long. The data in this field will be ids (each 10 characters long including comma and space). So I created two new fields - say CField A and CFieldB, which each will hold 40 characters (4 ids) long of data.
My Requirements are:
1. By default the second field CFieldB should be populated as N/A.
2. I enter the data (ids) in CFieldA. If there are more than 4 ids (i.e, 40 characters long), the extra ids should automatically get populated in CFieldB.

How I can achieve this. If should I use triggers, how can I use it? Are there any limitations with triggers? Mercury support engineer said that they don't support DB triggers, because one may encounter problems while trying to copy or upgrade to next version. Is there any workaround to it?