...
The only difference between MACRO("Rhino3",,,,) and and MACRO("Rhino4",,,,) is is that the first uses a single running instance of Rhino and the latter makes a new instance of rhino each time the function is executed (see Rhino Wiki). If you want to execute a script by a single running instance of Rhino, please use the "Rhino4.Interface" argument instead.
...
Please note that you can use this functionality in addition to the EXCEL#() function.
Documentation will be follow soon... In the mean time please contact Qnowledge for further details.
Quick links: Function Functions overview | Attribute overview | Constants overview | Dimensions overview