PIDs and their associated metadata can be made available in a machine readable format such as JSON or XML, via an API such as a SPARQL or OAI-PMH endpoint.
Persistence of the identifier depends on both the persistence of the external provider, and on your own organisation's ability to manage your local web pages, so if you change the web site all existing external identifiers will still resolve.
Given the expectation that any identifiers will persist indefinitely, once you have minted identifiers it is difficult to reverse that step. The things you have chosen to identify, and the format of the identifier are decisions that your organisation will potentially have to live with for a long time.
Some external providers expect that you will supply metadata for each item identified, so you will need to have tools that can deliver that information.
For more compatible identifiers, see Which persistent identifier does what?
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The National Gallery makes its collections available via an API in JSON, a machine readable format.
The Rijksmuseum in The Netherlands has a pilot implementation of a SPARQL endpoint for their collection data.
Consult the different aspects, from here you may want to look at Persistent, globally resolvable, maintained identifiers.