Supressing Fields in Sale Order

To make optional / mandatory you can use in IMG - S&D-> Basic > Functions-> Log of incomplete Procedures =>  select the fields > from the tables and the system will check for them (OVA2/VUA2)

To make a filed entry enabled or grey (non-entry allowed):

User exits in the program MV45AFZZ-USEREXIT_FIELD_MODIFICATION

This user exit can be used to modify the attributes of the screen  fields.

To do this, the screen fields are allocated to so-called modification groups 1 - 4 and can be edited together during a modification in ABAP.

If a field has no field name, it cannot be allocated to a group. The usage of the field groups (modification group 1-4) is as follows:

Modification group 1: Automatic modification with transaction MFAW

Modification group 2: It contains 'LOO' for step loop fields

Modification group 3: For modifications which depend on check tables or on other fixed information

Modification group 4: is not used 
The FORM routine is called up for every field of a screen. If you require changes to be made, you must make them in this user exit. This FORM routine is called up by the module FELDAUSWAHL.

With Compliments by: Taner Yuksel

Actually suppressing fielding sales orders userwise is quite easy. We are doing it in our company. For this we use userexit FORM USEREXIT_FIELD_MODIFICATION in MV45AFZZ.

Below is the sample code

IF SCREEN-NAME = 'VBKD-ABSSC'.

AUTHORITY-CHECK OBJECT 'ZMV45AFZZ' ID 'SCRFNAME' FIELD SCREEN-NAME.

  IF sy-subrc = 0. 
    SCREEN-INPUT = 1. 
  else. 
    SCREEN-INPUT = 0. 
  ENDIF. 
endif.

You place the authority check object in authorization profile in the role of the users, who should have access to the field (in this case it is VBKD-ABSSC), and there assign the corresponding fields that are to be accessed via this userexit.