Hi Tiffany,
I am not sure whether the feature you are asking for is available in terms of networking for any service. i.e., Can a service be programmed to use a x port if y is not available?
Logically thinking if any of the BO services start they can automatically pick random ports. When it comes to BO product, the CMS and SIA are to be provided specific port numbers which need to be bi-directionally available at all times during as well as post installation.
Auto-assignment is what you are looking forward to for CMS and SIA which I suspect SAP has not provided. Reasons; good connectivity and to avoid loss of communication is highly essential. The CMS and SIA are the most important services of BO; one is skeleton and the other is its body 
All remaining services can automatically come up with different ports;however, the cons which are usually observed is connectivity, network congestion etc. So auto - assignment would not be recommended