So as an example to do it explicitly, modify a view, click set rules for file display, click the import/export button, and paste this in the dialog
([=compare(length([Name]),>=, 64)]=1 or [=compare(length([Artist]),>=, 64)]=1)
Then click OK on all the dialogs to close them and modify the view.
The view will now include only files where either the Name or the Artist is longer than 64 characters.
You can add or remove fields from consideration by modifying the expression. To do one at a time, it would just look like this:
[=compare(length([Name]),>=, 64)]=1
and you replace "Name" with whatever field you want to test.
To do more than those two at once, keep adding in at the end (between the parenthesis) more clauses beginning with or, changing the field name each time. Like this:
([=compare(length([Name]),>=, 64)]=1 or [=compare(length([Artist]),>=, 64)]=1 or [=compare(length([Album]),>=, 64)]=1)
To truncate, select all the files you want to modify by using a shift click on the field you want to truncate. So for example, click the first file, scroll to the end of the list, and shift-click on the Name column of the last file. This will select all files in between.
Tap the F2 key. You are now editing that field for all files.
Enter the following
=Left([Name],64)
And all the Name fields will be instantly truncated to 64 characters. So be very careful. Ctrl-Z to undo.
You might want to make a library backup first if you aren't confident you know what you're doing.
So to sum up, you can search against multiple fields at once, but not all. You can truncate one field at a time.
I'm unsure why this is necessary: if the player has a limit of 64 characters, doesn't it essentially truncate long fields for you by not displaying anything longer, making all of this redundant? Or does it barf and refuse to import tracks with long fields? That would be pretty lame.
Good luck.