Changes to standard field length

Dear Experts,

I have a requirement as below,

Go to CAA3 Tcode. Enter details as below and press enter.

Go to Payments/Taxes tab,

Currently standard field 'Inc.Payt Method' highlighted above has length 1. Is it possible to increase this standard field length to 2? I am sure we can achieve this via access key. But is it recommended to proceed with this approach?

Kindly share your valuable inputs.

AWF