Does a site software upgrade re-set customized Default Scheme's (Item, Template, etc.)

[Mark Athas]

Jira Admin training suggests changing the default schemes when it will be very common that you want something different than the OOTB settings for all new projects.  It also appears that I can't set a 'customized scheme' as the default for new projects.  Question: Should the OOTB default scheme's NEVER be changed because your changes could be reset/removed/overwritten at some future release of the Jira Software product by Atlassian?