Can custom properties be exported to an excel spreadsheet, edited, and then imported back into the part files?

What kind of changes you need to do? May be you can edit them without exporting if you can explain with some sample files.

Alex,

You can use the SOLIDWORKS Document Manager API to read and write custom and configuration properties.

Yes you can but you must save your file before you try this at home.

• In the summary information tab you want to copy the custom properties from, move the mouse cursor over row number 1 (far left column); the mouse cursor should change to a right pointing arrow.
• Left click and hold then drag the mouse cursor to the last row (the window will scroll if there are more properties then window).
• Release the left click and press Ctrl-C
• In excel, select a cell and press Ctrl-V
• Delete the fourth column because that is the Evaluated Value column which SW automatically fills in.
• Make your changes in the third column.
• You can add a row but remember to set the second column to Text, Date, Number, Yes or No.
• Copy all the data
• In your SolidWorks document, delete all the custom properties currently there.
• Place your mouse cursor over row one and left click to highlight the entire roll.
• Press Ctrl-V.
• If I have written my instructions correctly, you should see your updated custom properties

So if I understand correctly, Alex, you want to export certain properties for all of the files in an assembly, all at once, to excel, edit them, then import those edits done in Excel back into the assembly and all of its components all at once, right?  This can be done. 

From Excel, you have to use the API calls to traverse the assembly tree and another API call to read each component's properties and write them to the cells in the spreadsheet.  If some of the properties are configuration specific, then you'll also need to capture the configuration name.  Writing them back may be a bit more tricky, but it involves doing the same thing except instead of reading the properties from each component, you would write the properties back with and API call.  Developing an algorithm like this can be tricky and may take some time, but if you have to do this a lot, it may be worth it.

Alternatively, have you thought about using a temporary indented (or parts only) BOM table of the assembly to edit the properties?  You can fairly easily edit the values in the BOM table and keep the data linked to the component properties, so it is essentially the same thing, but without the export import steps.  I'm not sure if the BOM table will write to general properties, but it definitely works for configuration specific properties.