Well there won't be any such modifications in the 35s since Lockmart will control the avionics code except in the case of the Israeli 35i which is a special case, and even then the Israelis are installing an overlay on top of the underlying OS.
The Japanese are going to replace the older 100 of their 200-odd F-15Js with F-35As. And by old we mean really old; their things are 70s relics with no Link 16 and still firing the Sparrow rather than the AMRAAM. The F-35A is therefore a very big time upgrade over that.
Meanwhile the remaining F-15Js will continue in service, being upgraded with more modern accoutrements like datalinks, advanced PESA radars, helmet cued missiles, countermeasures, etc
The current scheduled Japan F-35 buys are for around 40 of the 35A variant, but this will be extended to about 100 of the 35A and 40 of the 35Bs for operation from the Izumos.
Without more extensive modifications than just bolting on a ramp however, the Izumos, like the older US LHDs, aren't likely to carry more than 6 to 8 F-35s. If we do see them modded, it will probably involve a deck extension
There's a manga and upcoming movie about just such a ship, titled Aircraft Carrier Ibuki. It's extremely Rule 4 :D it models what an imagined Izumo extended deck could look like: