Unfortunately, there is way to do this OOTB AFAIK. Other folks can provide some clues may be if there is any option.
However, you can implement custom bulk metadata update functionality.
1- Implement a java backed webscript to generate the list of nodes refs and their current metadata in the excel sheet. This webscipt will read the folder node and find all files (even from within nested folders), and get the properties from each file/content nodes and write them into the sheet. You would get the row wise metadata/properties for each node. You must include the nodeRef in the sheet which will be used for updates later. You can write this sheet into logged in user's "MyFiles" directory, user can download the sheet from there and later upload a new version of it with updated metadata.
2- Implement an action on folders (folder-browse/folder-details) to allow generating the sheet which will be used for bulk metadata update
3- Implement an action on the Sheet which was written under "MyFiles", so user can then click to update the metadata in bulk after uploading the sheet with updated metadata as a new version of existing sheet.
4- Implement another java backed webscript which will update the metadata in bulk based on input sheet (generated as part of 1st step). It will read the existing node metadata/properties based on nodeRefs by processing row by row and then apply newly updated metadata by parsing the row for that particular nodeRef.
Note-Consider restricting updates to read only properties such as "created date,modified date,creator,modifier,node-uuid" etc. or any others based on your current business needs.
1- Implement an action in multi select action menu to select multiple files at once.
2- Implement a form that loads common and allowed (not restricted) metadata properties for updates
3- Use the ootb form processor to save the updates.