In order to use the new File Manager of 6.0.0r3 is it possible to use with older guest additions (in the guest) ?Each version of VirtualBox, even minor releases, ship with their own version of the Guest Additions. While the interfaces through which the VirtualBox core communicates with the Guest Additions are kept stable so that Guest Additions already installed in a VM should continue to work when VirtualBox is upgraded on the host, for best results, it is recommended to keep the Guest Additions at the same version.
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To disable this update check for the Guest Additions of a given virtual machine, set the value of its /VirtualBox/GuestAdd/CheckHostVersion guest property to 0; see Section 4.7, “Guest properties” for details.
For example on an old version of RedHat one could install older guest additions .... run it on a host with 6.0.0r3 and this will work...