Hi Ayrat
This method will not scale well and the task of keeping the Marketing Attribute in sync with the actual points value will not be easy.
As a more standard option take a look here: SPRO -Customer Relationship Management - Marketing - Marketing Planning and Campaign Management - Personalised Mail - Maintain Attribute Contexts for Mail Forms
Refer to the SPRO Documentation attached to this function.
This allows you to create a custom attribute which can be added into the Mail Form, similar to what you wanted to do with the Marketing Attribute. By using this mechanism you can code in the retrieval of the real time value.
Either option both involve coding, the above recommended mechanism will be quicker to code and far more reliable.
Regards
Arden