There are practical and political arguments against replacing Biden on the general election ticket. There are also practical and political arguments *for* doing so.

However, it is *not* the case that it is LEGALLY "too late" to change the ticket. The nominating conventions for major parties are held before every state's ballot deadline. Here's a summary of each state's laws, from the National Association of Secretaries of State (the people who run the elections).

https://www.nass.org/sites/default/files/reports/summary-ballot-access-laws-president-june-2024.pdf [pdf]