Can I update the maximum number of custom fields?

The maximum value for a custom field (100) cannot be updated because it is a global hard coded setting. Instead, you can use a JSON object to achieve the desired functionality. JSON is limited to 1MB per member which can hold a good amount of data. 

Steps to follow:

1. Access the helpful information provided here.
2. Follow the instructions in the documentations to learn how to use JSON for your custom field requirements.