It makes no difference if it's in the first week or not. It would just need to enter the top 10 at any period since being released to be counted as a top 10 single.
If there was another artist and they were really close in some sort of sales record, then a technicality like first week would come into play.
Oricon has lost all my respect tbqh, so this sort of stunt doesn't bother me in the slightest. I do think that it might not make it though... unless weekend sales are able to edge out the other singles...
It's not really rewriting history either
It's just adding to it
The first charting will still be recorded, it will just have a second chart life.
__________________
"Remember, don't let others dictate your music taste. If you like whatever you're listening to, keep listening to it."