Reduce number of columns of a result set from a Transaction in SAP system

The simple answer to your question is NO. Because, this is SAP standard behavior and if you want to restrict the number of columns to be returned then it will require you to change the original source code of SAP implementation.

The change will be quite exhaustive and it will also mean that you are violating the contract and hence, no support from SAP on any issue encountered later.

As you said you are filtering data that means the number of rows will not be huge and hence the number of columns will not have much implication on the performance of the transaction overall at a high level.

But if you do want to have flexibility that you require please opt for other way like SAP Query.