Can I hook into the plugin's functions?

Hello,

We want to make membership integrate with MailPoet (formally Wysija). I know the eNewsletter plugin does this, but my client does not want to change newsletter plugins.

What I need is a way to hook in and add steps when:

A new membership level is created.
Members are created, edited and deleted.
Members are assigned membership levels.

Is there are neat way to do this without editing source code?

Thanks

Helen