It is a bit of a hack, but there may be a workaround to this problem. In the "DOSBox for Google Chrome" app, the "C:" drive is currently hard coded to a normally inaccessible folder on a Chromebook (/data/c_drive). You can't get at this folder using the local file manager, but "DOSBox for Google Chrome" does provide a pair of import/export commands for transferring files between the hidden DOSBox folder and a local folder that Chrome OS's file manager can access (either the local Downloads folder or Google Drive).
It is not currently possible to direct the C: drive to a different folder and still retain the ability to import and export files, but it is possible to create a separate D: drive and map it to the Chromebook folder /data. This is a bit backwards from what is normally done, but what you can do is install WordPerfect on the D: drive and put all your data on the C: drive. You won't be able to import or export anything directly from the D: drive, but once WordPerfect is installed you probably wouldn't want to anyway. If necessary you could always copy these files back to the C: drive and export them from there.
It's not a perfect solution, but it is at least somewhat workable. Here are the settings to add to the "DOSBox configuration file" on the "DOSBox for Google Chrome" setup page to make this work (note, the mount command paths are case sensitive).
[autoexec]
mount c "/data/c_drive"
mount d "/data"
d:
The only thing I don't know is exactly how you installed WordPerfect and whether it is possible to install it directly to the D: drive. You may have to first install it to the C: drive and then copy it over to the D: drive. But i suspect you can probably figure that part out.