Greetings Avnikant,
Interesting query! There is no t-code for WCDs akin to IPM2 for us to use... In principle, if you want to change the Approvals on a WCD, then the user would have to have the access to Change the WCD. I feel it will not be possible to segregate this based off the standard.
One possibility could be to try to record an SHD0 Transaction Variant of the t-code WCT7 and disable or hide all the fields and function codes, apart from the one relevant for the Approvals.
Another possibility is to use BADI_WCM_WCMOBJ and see if you could use methods such as CHANGES_FORBIDDEN, FCODE_DEACTIVATE, FUNCTION_AUTHORIZATION_CHECK, SAVE_CHECK to prevent certain users from changing fields or accessing function codes. I expect a custom authorization object would also be required.