No the vanilla DD item cannot be changed . It is never recommended . In our case , there was such requirement to have some large fields like Marketing description , allergy information etc (in food business ) , so we create custom item tag and it has item # and other custom fields of larger description sizes as needed by business , custom application and reports .Our ecommerce gets info from there for web customers and mobile too
Custom UBE to see everyday using outbound interoperability in F4101Z1 to see new items added and create entries in the custom tag to keep in synch always . Mass update application with grid given to business to update the records what they want .
As others have said, the short answer is no. It has been tried before and always ends in tears (very expensive tears).
As is mentioned, you can look at text attachments or a tag table mod. Another option to consider is AMS (https://amseam.com/) have an OVI extension that provides searchable 3000 character description fields for the item master.