You can at any time access variables of other projects in the same workspace with normal dynamic elements.
Now the variable selection dialog opens.
Here you not only can select variables from the I-PRO, but in the left area you also can select other projects. You will then get the variable list of the according project and can select variables from it.
As the I-PRO is a client to the server PRO1, this will work without any problems in the Runtime.
The control system does not care, whether the network structure in the Runtime really allows access to the selected project and its variables!
For example, you can select a variable from the I-PRO for the start picture of the project PRO1 in the Editor. But this will not work in the Runtime!