When the dispute case was been closed, it's been regarded can't be changed anymore by users at the front-end. The user will get the below message when clicking the change icon:
The FSCM system could set the status as 'Closed' (SCMG_T_CASE_ATTR-STAT_ORDERNO) and close the dispute case automatically while the disputed amount is updated as ZERO when the related document is clear.
It's a standard process, but FSCM does allow closed dispute cases re-open if any new attributes need to be updated through FM: 'BAPI_DISPUTE_ATTRIBUTES_CHANGE' especially when the changes come from an external system.
Maybe it'll be better to create a brand-new dispute case sharing the same accounting document or other key info as the previous one like the DCD case. It depends on aligned sync methods when an external system is involved.