Huckleberry wrote:

Regarding aliases that are created on my computer, for example the
alias used when I add a new person to my address book, can I change
the alias?

You'll have to tell me what you mean by "alias" here. The usual definition
of aliases are multiple email addresses that all point to the same mailbox
on the server. Clearly, you have no idea whether or not your contact's mail
addresses are aliases.

Can I change all instances of it for past messages? That
is, if I change an alias, then I assume that the change will be
reflected in future messages that I send, but will it also change the
alias in sent messages?

Until I know what yuo mean by "alias", I won't be able to answer this.
--
Brian Tillman [MVP-Outlook]