I would have thought that if it has been set up correctly for the AT95e then you would not need to make big adjustments to the VTA if you replaced it with the Ortofon.
Unless there is a significant difference in the height of the cartridge body, if there is then spacers may be required.
When getting a replacement take along the AT95e and do a quick eyeball of the body height against the cartridge you intend to purchase. Might I suggest you go for the 2M Blue if you can afford to or even look at the Grado Prestige Gold which will go very well with the RB300 arm.
Adding spacers, if necessary, is easier with the old RB300 arm as compared to the new version. It is simply a matter of disconnecting phon cables from your amp and unscrewing the large octagonal nut from the underside of your arm then lifting arm straight out. Put on your spacer and place arm back in the hole. Re-tighten the nut slightly and check your VTA - you may have to do this several times to ensure correct thicknesss of spacer has been chosen,. When you are satisfied fully retighten the nut.
You can, if you so wish do away with the hassle of washers by getting a Michell VTA Adaptor for about £18 (do a quick Google search). This is a threaded adaptor that you fit in place of the washers and which can be adjusted by very small amounts as required. It's a lot simpler and certainly worthwhile if you see yourself changing / upgrading cartridges in the future. Having said that, if you are, then I would also go for a Michell Fingernut which replaces the awkward sized octagonal locking nut and is much easiler to tighten up using fingers alone. Happy upgrading!