Tax on what you invest in
Nothing is taxed while it sits there. The bill arrives the year you sell - which makes the year you sell, and the units you sell, decisions rather than accidents.
Long-term gains on listed equity carry an annual exemption that does not roll over. Left unused it simply expires. And within a folio units leave first in, first out, so the gain you realise is decided by which folio you sell from.
The exemption you do not use expires
A holding that doubles over ten years is taxed once, in the year you finally sell. Do nothing and the whole gain lands in a single year, well past any annual allowance.
Harvesting is the alternative: sell enough each year to realise gains inside the exemption, then buy straight back. Nothing changes about what you own - but the gain has been booked at no tax cost, and your cost base resets higher, which shrinks the bill on everything that follows.
No. Loss harvesting books a loss to set against gains. This books a gain deliberately, to use an exemption that would otherwise go unused and to lift your cost base. Different moves, both with their place.
Folios decide which units leave first
Within one folio, redemptions follow first in, first out. Your oldest units go first, and those usually carry the largest gain. You do not get a say.
A second folio in the same scheme has its own queue and its own cost base. Redeem from the newer one and you realise a smaller gain; keep the older one for a year when you want to use the exemption. Same fund, same money, a different tax outcome.
No. There is no transfer - you would have to redeem and reinvest, which is itself a taxable event. Which is why the folio structure is worth deciding before you invest rather than after.