I'm pretty sure I was able back then to easily set up both mist and geth with (almost any supported) specific version number of these software:
The trick was just to copy the geth binaries somewhere in the %APPDATA% directory (you will easily see / recognize where the "correct"/normal version of geth will be after a standard installation, just search for geth.exe within that directory). So the idea is to just replace the "other" version of the geth folder/installation with the version you want to test from https://github.com/ethereum/go-ethereum/releases
Futhermore, I had to disconnect from the internet, otherwise mist/geth would both try to update to a newer version (there is a clientBinaries.json file or similar that will be queried on the net on startup).
To me 6.4 seems to be way too old, honestly. because as we can see here, mist 8.10 was using geth 1.6 (https://github.com/ethereum/mist/blob/dc...aries.json).
so the claim about geth 6.4 seems to be very strange to me.... maybe you had it install, but I'm not sure if mist would use it or even be able to use such an old version, I doubt that (but in any case you can try to contact the Mist devs or geth dev team etc and try to double check which version were compatible and used by default).
Internet connection is not needed and NOT recommended because of the 2 main reasons mentioned above: it tries to update and the sync with blockchain etc is NOT needed to check a password... you can have no chain data and still check if you can unlock the account as far as I know.
Attention: I think it's almost needless to say but it's VERY important that you of course should make a full backup of all the important files, especially the json files, but not only... best would be a full backup of the ethereum-related mist/geth folders in %APPDATA% or all those files under C:, or even better a full backup of the whole disk (HDDs are cheap nowadays and it's best to have a safe copy, just in case)... before you make any new installations or changes to the mist/geth versions/installations/configurations etc. Backups are always worth it! best on a completely different/separate HDD/SDD/USB thumb driver or similar. Don't try to use any shortcuts here. Back'em up !
BTW: the folders for Apple Mac systems seem to be:
* ~/Library/Application Support/Mist (mist configuration ?)
* ~/Library/Application Support/Ethereum Wallet/ (only wallet data ?)
* ~/Library/Ethereum/ (only geth software and data ???)
* ~/Library/Ethereum/keystore (the JSON / keystore files ?)
as you can read in the mist wiki: https://github.com/ethereum/mist/blob/ma...xt#L32-L42 , https://github.com/ethereum/mist/blob/ma...fig-folder , https://github.com/ethereum/go-ethereum/...lts.go#L64
The trick was just to copy the geth binaries somewhere in the %APPDATA% directory (you will easily see / recognize where the "correct"/normal version of geth will be after a standard installation, just search for geth.exe within that directory). So the idea is to just replace the "other" version of the geth folder/installation with the version you want to test from https://github.com/ethereum/go-ethereum/releases
Futhermore, I had to disconnect from the internet, otherwise mist/geth would both try to update to a newer version (there is a clientBinaries.json file or similar that will be queried on the net on startup).
To me 6.4 seems to be way too old, honestly. because as we can see here, mist 8.10 was using geth 1.6 (https://github.com/ethereum/mist/blob/dc...aries.json).
so the claim about geth 6.4 seems to be very strange to me.... maybe you had it install, but I'm not sure if mist would use it or even be able to use such an old version, I doubt that (but in any case you can try to contact the Mist devs or geth dev team etc and try to double check which version were compatible and used by default).
Internet connection is not needed and NOT recommended because of the 2 main reasons mentioned above: it tries to update and the sync with blockchain etc is NOT needed to check a password... you can have no chain data and still check if you can unlock the account as far as I know.
Attention: I think it's almost needless to say but it's VERY important that you of course should make a full backup of all the important files, especially the json files, but not only... best would be a full backup of the ethereum-related mist/geth folders in %APPDATA% or all those files under C:, or even better a full backup of the whole disk (HDDs are cheap nowadays and it's best to have a safe copy, just in case)... before you make any new installations or changes to the mist/geth versions/installations/configurations etc. Backups are always worth it! best on a completely different/separate HDD/SDD/USB thumb driver or similar. Don't try to use any shortcuts here. Back'em up !
BTW: the folders for Apple Mac systems seem to be:
* ~/Library/Application Support/Mist (mist configuration ?)
* ~/Library/Application Support/Ethereum Wallet/ (only wallet data ?)
* ~/Library/Ethereum/ (only geth software and data ???)
* ~/Library/Ethereum/keystore (the JSON / keystore files ?)
as you can read in the mist wiki: https://github.com/ethereum/mist/blob/ma...xt#L32-L42 , https://github.com/ethereum/mist/blob/ma...fig-folder , https://github.com/ethereum/go-ethereum/...lts.go#L64