Beside Account and Excel in-house you can create other in-house series with Macrobond:
If you need one-time data that will be accessible only in that file it's what you were looking for. Its prefix is ih:mb:doc. For more information see Document series – adding external data.
If you have a calculation in one place/file and want to use it elsewhere then you can create calculated in-house which will save an entire file with series needed for this calculation. It can be edited later. Its prefix has double naming (for file and series) ih:mb:priv:calc1:series1. For more information see Calculated in-house series – saving your own calculation.
You can also use in-house data from other sources like Bloomberg or from your own SQL database. Note that both need enabling special connectors within Macrobond main-app. For more information about these solutions see The Bloomberg Connector and The SQL Database Connector.