Hi Kumar,
Your requirements are exactly what we are doing in our current upgrade project. Please find my answers:
1. Client is planning to discontinue the use of UNSPC product category and replace them with Proclass
Ans: Yes, it is fine. You need to focus on following points.
a) In upgraded system, you would need to control the access to only ProClass categories using SRM org structure
b) You can have new PGRPs for this new ProClass structure and try not to use old PGRPs
c) Don't rename the old UNSPSC categories as this will affect reporting on old spend
d) Rework on mapping for Punchout catalogs
e) Can also use category hierarchy for level-1 and level-2 ProClass and only create material groups for last level.
2. Map product categories to vendors to determine the combination for buying purpose
Ans: We have done it through SRM central contract/ vendor lists where the client has created category contracts or vendor lists against ProClass and we have restricted the use of independent vendors which don't have active contracts/VL.
Go ahead! its all working. I don't see any risk.
Cheers,
Ravi Pachauri