Multiple customer groups per customer

Question

Can I place customers in multiple customer groups in Magento?

eg. "Dupant" client in the "Wholesale" and "Retailer" groups.

Answer 1

There is a similar question here: assign a client to multiple customer groups in magento .

However, I'm not sure if the answer provided is universal, because the following snippet

$customer->getGroupId()

it is used quite a lot in the Magento kernel, where it is also assumed that the group identifier returned from this method is an integer, not a string (a list of identifiers separated by commas).