Modifying stream entries

Hi,

are there any built in services that allow you to modify stream & value stream entries? We have a requirement to remove all customer/user data upon request. However, we would like to retain some of the data we hold to aid in data analysis and so we are looking to modify that data if possible so that it cannot be connected to an individual customer. I can see that there are services to purge/delete entries which we will use in most cases, but there are other circumstances where we might wish to retain the event. 

Examples of this might be:

Streams: where we record a 'log in' event on a remote asset. The data for that event holds the username. If possible we would like to keep the event, but overwrite the username value with some anonymous data.

Value Stream: where we log the name of the current 'job' being carried out on the remote asset. This might be customer specific.

One thought that we had was to add a new entry (with modified data) using the old event timestamp and then delete the old event, but I would be concerned that this might have unexpected consequences on the stream (i.e. performance etc.). However this would only apply to the stream thing as far as I can see.

Thanks in advance.

K