Hi Greg .. I am not sure I fully understand what you would like the cbioportal website to do when you say "parse" ICD10 codes. I think there would be no problem in adding a clinical attribute for your samples which contained a list of ICD10 codes with whatever list format you choose. These lists could be retrieved as clinical data through the API or viewed through the website UI. However, they would simply be strings attached to identified samples in your sample clinical data.
It would be possible to create your own set of codes to represent cancer types and construct a database which holds those codes in the type_of_cancer table, but that would take some work. Also, the codes from that table must form a strict tree structure with parent-child links between all nodes. But I do not think the cBioPortal code base supports the use of multiple cancer type codes for a sample or for a study. We do have a special code "mixed" which we use for studies which combine samples of various cancer types. https://oncotree.info/#/home?search_term=(MIXED)
And lastly, we created a tool to convert oncotree codes to/from ICD0 codes (as well as other ontologies). You can see the details here:https://oncotree.info/#/home?tab=mapping
under the section Ontology to Ontology Mapping Tool
I hope this information is helpful.