ME12: Purchasing Infor Record - User Exit

Hi Gurus.

Is there anyone who knows a user exit that I can use to block the editing of Infor Records directly from the screen fields ME12. The requirement is to bar users from editing the following fields directly:

1) RM061-LTEX1,

2) RM061-LTEX2,

3) RM061-LTEX3,

4) RM061-LTEX4,

5) RM061-LTEX5.

The users alternatively wanted the fields to hold more than 40 characters.

Any ideas on how this can be done?

Points will be awarded.