I have seen most of question related to make some field display, hidden and input only. So this document helps them to make desired file disable and input as per the requirement without using screen variant and transaction variant. It is applicable only those for those program whose screen group is provided by SAP.
Go to that screen onto which you want to make any field disable, input and hidden. Then Select System-Status and copy the program name from there.
Then Go to t-code OQFA and the give Module Pool name as program name.Then click on change It will reach you at Field Selection Screen Group.Then select the desirable screen group and click on Modifiable. and make the desirable field as input display and hidden.
You can use Influencing Button if you want these change to particular thing like inspection type, notification type.