I'd like some advice on a deployment strategy. If a development team creates an extensive framework, and many (20-30) applications consume it, and the business would like application updates at least every 30 days, what is the best deployment strategy?

The reason I ask is that there seems to be a lot of waste (and risk) in using an agile approach of deploying changes monthly, if 90% of the applications don't change. What I mean by this is that the framework can change during the month, and so can a few applications. Because the framework changed, all applications should be regression-tested. If, say, 10 of the applications don't change at all during the year, then those 10 applications are regression-tested EVERY MONTH, when they didn't have any feature changes or hot fixes. They had to be tested simply because the business is rolling updates every month.

And the risk that is involved... if a mission-critical application is deployed, that takes a few weeks, and multiple departments, to test, is it realistic to expect to have to constantly regression-test this application?

One option is to make any framework updates backward-compatible. While this would mean that applications don't need to change their code, they would still need to be tested because the underlying framework changed. And the risk involved is great; a constantly changing framework (and deploying this framework) means the mission-critical app can never just enjoy the same code base for a long time.

These applications share the same database, hence the need for the constant testing. I'm aware of TDD and automated tests, but that doesn't exist at the moment.

Any advice?