We are not able to manage individual DNS entries as the current API only supports overwriting the entire zone, which means that for each individual change we have, we would have to repopulate the zone. On the other hand, there is no way to fetch the current zone (that is: all the current records).
So, in practice, it's not possible to update a single record without locally storing all the zone records, which doesn't make sense.
Can you please provide a solution for this? I'd just go for a single DNS record update by maybe extending the existing one with a flag whether we are updating an individual record or the entire zone.
26-02-2020: We've implemented this feature in our brand new REST-API. For more information, see https://api.transip.nl/rest/docs.html#domains-dns , https://github.com/transip/restapi-php-library/blob/master/src/Repository/Domain/DnsRepository.php , or our PHP REST tutorial that demonstrates this: https://www.transip.nl/knowledgebase/artikel/377-rest-api-automatische-authenticatie-in-php/ or https://www.transip.eu/knowledgebase/entry/377-transip-rest-api-automatic-authentication-php/