Well I think we know what you mean, but "green wire mod" refers specifically to cutting the green wire in the battery tray which is designed to hold 8 AA cells. If you are using LiPo cells, then you cannot be using that battery tray, so there is at the outset no green wire to cut. To inhibit charging, you would have to provide a green wire and arrange that it has a suitable voltage on it, either by connecting to an intermediate cell or by using a voltage divider.
Indeed so, but if you do have protected cells, why bother with the green wire? Why not leave it out, and let the FT-817 charge the battery if it wants to? As soon as one cell reaches the fully charged state, it will stop safely.
You probably do want an external charge connector so that you can balance the cells from time to time, and possibly charge them faster than the FT-817 can. But I see no harm in letting the radio charge them. It will provide a useful and convenient top-up charge. Clearly you mustn't use both charging methods at the same time (I presume this is why the battery tray that started this thread provides a switch).
Obviously with unprotected lithium cells it's a really good idea to provide the green wire signal if there is any possibily that you will connect external DC with the batteries still in circuit.