A regime switching model is a model in which the parameters may change every few periods, e.g. medium term cycles in macro (expansions and recessions). Here you build one (Markov Switching) model that generates short to medium term cycles over time. Structural change is by definition very infrequent as it happens over longer terms (20-50 years). In this case the data migrate from one model to another and you are not expecting to have more than one or two such migrations in a typical data set...
The adoption of new technologies, such as the shift from analog to digital communication systems, can lead to a structural change in the way that information is transmitted and processed.
A change in policy, such as an increase in the minimum wage, can lead to a structural change in the labor market, affecting the demand for and supply of certain types of workers.
A demographic shift, such as an aging population, can lead to a structural change in the social and economic landscape, as the needs and preferences of different age groups may change.
Here are a few examples of regime shift:
A sudden shift in the climate, such as an abrupt increase in temperature or a sudden change in precipitation patterns, can lead to a regime shift in an ecosystem, affecting the distribution and behavior of different species.
A financial crisis, such as a stock market crash, can lead to a regime shift in the economy, as it can affect the availability of credit, the value of assets, and the overall level of economic activity.
A political regime shift, such as a revolution or a coup, can lead to a rapid change in the way that a country is governed and the policies that are implemented