Seems an OK change to me.
I only learnt that Hayling Island was twinned with Gorron when I cycled through Gorron itself!

Not quite sure what you are trying to acheive here. Langstone Bridge (in various sections) is already in OSM.
Changing/modifying complex things can be difficult without more experience in the OSM ecosystem.

Fairly sure the addresses are available in the building outlines, so there's no loss of information.

I don't think I used it, but IIRC it looked fairly new.

👍
Re: Axe Road bit - looks like you can go south down to Brue Avenue; I remembered specifically that going north into Axe Road was not possible.
Somerset Bridge road layout seems to changed considerably, so the current mapped junction is not representative. This road probably needs a separate survey.
I'm based in Portsmouth so unlikely to do any of these follow up edits any time soon.

I placed the node outside; thus the drinking fountain is available 24/7.

Yes. From what I recall the defibrillator is outdoors of the main building (not currently mapped - possibly the town hall?) in the central square.

Colehill! Not Coleford.

So how would you record the ground truth version as in the name on the road sign (since the 'name' has the full expanded version)?
Guidelines are guidelines - not mandatory rules - so some flexibility is there for atypical situations.

Um, why did you delete this?
What harm could it be doing?
The 'alt_name' is exactly the text on the street sign.
Also this is the name used in OS Locator dataset and thus useful for comparing OSM vs this other dataset.

The edit is good.

Even better would be to add bicycle=yes & foot=yes as well since cyclists + pedestrians can use this ferry too.

You may want to consider checking at least for 'source:ref' tags.
At least Brunt Acres Road is signed on the road as C32.
From http://www.flickr.com/photos/pobice/3432837568/ back in 2009 and it's still there as of August 2018 when I went past.

A cursory look at other sources such as Bing, OS_OpenData_Streetview & NLS OS:1:25K sources suggest this is a track/service road to an isolated place in the middle of the Welsh hillsides.
Clearly bridleway is closer to reality than an unclassified road, although personally I would have made it a track.

You need to also delete the original amenity=bank tag too.

If you are changing such a large number of things over a large area, please describe the nature of the changes in the comment changeset for future reference and understanding.

I think the postboxes in the Postal Musuem such as:
node/4939823803
Would be better described as historic=post_box rather than amenity to prevent confusion over such postboxes being actively in use for postal services.

No not especially, as I passed by relatively rapidly on bicycle.
Saw some old Yew trees in Powis Castle Gardens the next day though (not mapped yet either).

I believe historic=memorial is more appropriate than a monument for plaques.
A monument is normally something quite big (e.g. the Naval Memorial on the seafront)

Fairly sure I didn't add them, e.g.
relation/5465217/history
However I may try to fix them in time...

Yes indeed I moved it, as can be seen fairly clearly on Bing aerial imagery - which aligned to my GPS trace (albeit that ended on path entrance to the pub garden).
The Code stones are directly in line from that path entrance at the back of the pub garden.