Would it be possible on an iPad to change the "from" entry on an email to another account when sending the email?

Of course Yes. On iPad or iPhone from can be changed only if you have multiple accounts added to the iOS mail app.

Simply compose a new email, tap on CC or To or From

And then tap on From to change the account

Yes it is. The requirement to make this work is that the other email address has to also exist as an account in the Mail app. For example, you can setup an email account with hotmail.com and one with gmail.com and add them to the Mail app. When you choose to write an email then you can click on the From field (Click on the appearing email address) and your other email address(es) will show as options to use.

Axel F.

Also, the from address auto-selection is based on where you are choosing the new mail option. See the pic below which is self-explanatory. This is valid for iPad and iPhones too.