Just to clarify, is this the correct sequence of events?
You had originally bought and collected an Advance ticket for a journey on 4th Novemeber from Manchester to Euston. Then you needed to change the ticket to an earlier train, for which the procedure appears to be slow. Since you were worried that the Advance price for the earlier train would become too expensive for your taste (in particular the walk-up fare is not acceptable) by the time the procedure finishes, you decided to just buy a new Advance ticket for the earlier train.
As for the unused original ticket, you wanted to make use of its value on a future journey instead. You would like to make this future journey in January, but the original ticket must be exchanged before the original travel date on 4th November (you incorrectly wrote "4th Jan" in your post #30), by which time Advance tickets will not yet be released for your desired journey in January, so you would only be able to exchange the ticket for (part payment towards) a walk-up ticket, which is too expensive for you.
So the question now is how to not let the value of your original ticket go to waste, without being forced to buy a too-expensive walk-up ticket?
Firstly, are you sure you can't just refund it? Wallsendmag's reply #2 seems to imply this is possible (but you have to post the ticket back). From what I can tell on
Avanti's "Train Ticket Refunds" page "Refund information" -> "I have an Advance ticket" -> "Bought your ticket on our app or website?" -> "If you are requesting this refund before 6pm the day before travel then please fill in this refund form", there is no indication that collected paper tickets cannot be refunded. (But if you go down the
change-of-journey route, rather than refund, then you do run in to the restriction "Only E-tickets and uncollected paper tickets can be amended".) Note that the
linked form is a generic "Send us a message about refunds" form, so make sure to say explicitly that you would like the ticket to be refunded.
Secondly, if not refundable, could you not amend the ticket to some future date in between where the advance ticket price matches the value of the original ticket (so you don't have to put more money in, and don't let any value go wasted), and then amend it again later to the actual journey you want?