Calibre's Implicit Max Limit for Valid Values for a Custom Field?

[DaltonST]

See the attached .jpg file. I created a custom Book Genre field with the type of "Text, but with a fixed set of permitted values", and populated it with comma-separated values pasted in from the attached .txt file. Works great except for one problem. Calibre only allows 775 comma-separated values to be pasted in. I have over 2,000 values for Book Genre derived from the publishing industry and then standardized for use specifically in Calibre as a replacement for Tags, which cannot have any predefined valid values and hence are dynamically itemized by existing random book Tag values.

Question: How could I increase the maximum value of comma-separated values for a custom field of the type shown in the attached .jpg file? Could anyone please point me to the .py file within the Python code for Calibre 1.36 where the array size might be found for custom field types of "Text, but with a fixed set of permitted values"?

Thanks in advance for your help.