Hi Suhas ,
We can give a try by using formula variable and a key figure with if condition . Sort based on key figure and hide it.
1. create a formula variable to read material key .
2.create a key figure if material key=mat03 then 1 else if material key=mat04 then 2 else if material key=mat01 then 3 else if material key=mat02 then 4 else 5 .
3.Apply ascending sort on key figure.
this approach can be usable there are only few items( less than 10) else it may leads to performance degrade .
Consider your front end before doing this . if it BO then we can easily do at BO .