As of Nuget 2.8 there is a feature to downgrade a package.

Nuget 2.8 Release Notes

Example:

The following command entered into the Package Manager Console will downgrade the couchbase client to version 1.3.1.0

Update-Package CouchbaseNetClient -Version 1.3.1.0

Result:

Updating 'CouchbaseNetClient' from version '1.3.3' to '1.3.1.0' in project [project name].
 Removing 'CouchbaseNetClient 1.3.3' from [project name].
 Successfully removed 'CouchbaseNetClient 1.3.3' from [project name].

Something to note as per crimbo below:

“this approach doesn’t work for downgrading from one prerelease version to other prerelease version – it only works for downgrading to a release version”

Source: http://stackoverflow.com/questions/10206090/how-to-install-an-older-version-of-package-via-nuget