Hi,
To disable fields in MRP1 as described then you will either have to do it programatically or use another technique such as a transaction variant which is linked to a custom tcode and assigned to a subset of users through their role as a substitute for MM01.
In the transaction variant you can set certain fields to be display only or hidden however with transaction variants they are often easy to break and be navigated around, the impact of which will depend on how important this data is.
There is some more info on tx variants here: Transaction and Screen variants with an Example