Enable for input erroneous field after the E error message in MIRO?

I'm developing a validation in tx MIRO through the BADI MRM_HEADER_CHECK, I show a message when the field "reference" has already been used. The message has type E, this disables every field on screen and so the user can't return to that field to fix its value.

FYI:

• I have to show message type E because I want to block every fields excepts the two fields with encircled in red. I saw that the people suggestion use this:

• if I put the breakpoint SY-DINNR equals to 6000.

• In my BADI code LOOP AT SCREEN doesn't see field names that I want to disable.

• MESSAGE <msg> TYPE 'S' DISPLAY LIKE 'E' doesn't work as well

I can't modify code that is out of my BADI code, e.g. in PAI and PBO modules:

CHAIN.
  fields: f1,f2,f3.
  MODULE <mod name>.
ENDCHAIN.

This my BADI code:

*This field symbol have the values of inputs.
ASSIGN ('(SAPLMR1M)RBKPV') TO <fs_rbkpv>. 
IF <fs_rbkpv>-XBLNR = lwa_bkpf-xblnr.
  MESSAGE lc_message TYPE 'E'.
ENDIF.

Any ideas? Thanks in advance.