how can we have a custom solution than can help to manage the MCID my on org
We wanted to have our own ID and Adobe Analytics / AAM etc and also to all the respective systems we have so we have unified ID in all the systems
You can set your own ID (aka declared ID, customer ID, CRM ID) together with ECID to map them to each other. Read this article https://docs.adobe.com/content/help/en/id-service/using/id-service-api/methods/setcustomerids.html
This will allow to enrich and merge profiles in AAM, to enrich data in AA.
However, this will not allow you to stitch the cross-device visits in AA. If that was the intention, consider either Customer Journey Analytics (if I am not mistaken this requires Ultimate SKU/ license) or use s.visitorID variable, but it's not recommended.
Hey it is possible with your Own ID (consists CRM ID, Customer ID). Read this article more useful information https://docs.adobe.com/content/help/en/id-service/using/id-service-api/methods/setcustomerids.html The process mentioned in above article to enhance the merge profiles in Adobe Analytics Do remember one thing that you will not allow to stitch the cross-device visits in AA.