Add with PowerShell one health service to a Run As Account / Distribution

Hi Chaps,

I want to add a new element to the distribution list of one Run As Account. 

If I use Set-SCOMRunAsDistribution adding a new element, the objects that were there will be deleted and only appears the new one. So what I'm doing is add every time the complete list of Health Service that they should be there.

I wonder if there is other way to add a new element to the list without delete the tenants.

Thanks in advance.