Payment Block Validation for User group

Dear SAP Validation Expert,

We like to allow only selected FI users to change Payment Block to ' ' (Free for Payment) in tcode: FB02, FB03 and FBL1N.

Curently we have managed to block other un-selected users from changing the Payemnt block to Free for Payment.

But our issues are Other fields also NOT able from changing/maintaining. For example in FB02, user NOT able to change Payment Block (BSEG-ZLSPR) from 'B' to ' ' (Free for Payment) which is expected but user also NOT able to maintain other field such as Payment term(BSEG-ZTERM), Baseline date (BSEG-ZFBDT), Assignment (BSEG-ZUONR) and Text Field(BSEG-SGTXT).

Below is our Validation, please advice how to improve it so that other fields can be changed too. Your swift reply is very much appreciated.

Pre-requisite:

( ( SYST-TCODE = 'FB02' ) OR

( SYST-TCODE = 'FBL1N' ) OR

( SYST-TCODE = 'FB03' ) AND

( BSEG-ZLSPR = ' ' ) AND

SYST-UNAME <> 'HIS20083'

Check:

BSEG-ZLSPR <> ' '

Message: E: You have no authorization.