For downloading, go and look on the internet for Flickr Downloadr, which is cross platform through Mono for Linux as well as Windows. This can be made to work some of the time, but I am seeing constant crashes when working with some of my larger albums. The biggest problem with this software is you can only download one album at a time, and often it will crash partway through the download, forcing me to download 100 photos at a time.
Still, so far I have downloaded more than 10% of the 55,000 photos on this account with this software.
Then, to upload again, well you can use the built in upload web page, which constantly has timeout errors, or pay $6 for a 1 month pro subscription which gives you access to the Uploadr app. Which is what I am doing. This is pretty reliable, but it will still take all day to do the upload, maybe longer.
So I hope the download will be all completed today, and maybe the upload to the new account will take 24 hours or something. Then I can delete the two old accounts and just keep the two current ones.
Apart from the downloadr crashing every few albums I have deleted the first batch of uploading twice, this is due to having some albums that contain large numbers of photos some of which are duplicated, and the idea is that as the uploadr can deduplicate, it gives me a chance to remove some duplicates automatically at the same time.
The Flickr Downloadr software while good when it works has obviously suffered from a lack of resources, with the download package not updated in 10 months, and no new packages from the package repository, with xenial being the last supported version of Ubuntu. Hence I doubt these bugs will be fixed any time soon.
UPDATE: Unfortunately Flickr Downloadr has turned out to be a bigger piece of crap than I thought, just completely refused to work after downloading about 25,000 images so I have to come up with a way to get the rest downloaded. Probably will have to get the originals from somewhere else like the Picasa albums I downloaded from Kahukowhai last week.
Meanwhile Flickr Uploadr has some kind of inbuilt history that I can’t get rid of because I have uploaded everything and then deleted it again and now it says everything has already been uploaded when it hasn’t. LOL. All very messy.