Well, probably. Technically the airside transfer buses are for those with a connection, not terminating. Now, I've never known anyone check to see if you have an onward boarding pass, but it's not totally impossible they might do so. The risk is low of you not being allowed on, it's just that sometimes the queues might be anything up to 30 minutes. You still have to clear immigration and customs at T4 when you get there, and having not done that for a while I'm not sure which typically has the worst queues - although my inclination would be T4 because (a) the immigration area hasn't been refurbished as recently as T3 and (b) the demographic of passengers arriving there is probably more time consuming for an immigration officer than at T3. I would personally still clear at T3 and take the landside transfer options.

Obviously to even attempt an airside transfer you'll also have to be travelling without hold luggage because that will be delivered to your arriving terminal, and won't be accessible to you if you switch terminals given it remains in the secure area behind customs.