At the moment merging, splitting or otherwise changing apple ids is very difficult (in most cases impossible). I honestly think you are going to struggle to do what you want.
I'm sure that Apple would suggest that you use home sharing to share your library. If that is not possible (ie the family member doesn't live in the same house) then I imagine their response would be that you shouldn't be sharing your library in this way anyway.
If you were to create a new apple ID solely for match then all your tracks should still work on it, just not showing up as purchased. However, you would still need to share your new ID and password with the other person and therefore they would be able to be make purchases on that account.
Personally, I don't think that match is the way to go other than with extremely close relationships (ie husband and wife)
I don't mind giving out a user/pwd for the itunes match also allowing for purchases to be made. The family member is my spouse so that is not a problem but I don't want to give out my @me pwd because I use that for business emails etc which are sensitive.
I have already set up itunes match but that is all now linked to my @me address. I thought purchases were directly linked to the itunes id ie my @me address so how will they play if I create a new itunes store account and go through the itunes match process again because it will not be linked to purchases that were made using the @me address.
I understand the concept of the home sharing but that requires my itunes app to be open and that is on my laptop and there are times when I am away on business etc and therefore not good because the itunes library will not be accessible unless my laptop and itunes is open on the home network. This is why I would like my spouse to be able to access the itunes match library at any time and from wherever. I dont mind having a new itunes only appleid but what happens to my existing itunes match library associate with my @me account and to purchases that have been bought over many years using that @me account? I want my spouse to be able to plug in the ipod and sync to the itunes match library too.
As I understand it, if you have already subscribed to Match on your existing ID then that can't be changed. You have two options as I see it.
You could set up a new iCloud account and start using that for your personal stuff. I imagine that will be a lot of hassle, and would still leave your email history available on the old account. Overall I wouldn't recommend it.
The best solution I can this of would be to accept that you have wasted the $25 you have sepnt on Match so far, turn it off and resubscribe with a new ID. You could then share that ID with your wife.
The downside, other than wasting $25 would be that your purchases on your old account would be shown as Matched, rather than purchased in the cloud. Unless you are near the 25,000 limit then that shouldn't be a major problem. As I understand it, iTunes will still allow them to match, even if they are purchased on another account.
If you have any music purchased a long time ago (pre iTunes+) then you may encounter problems with those files, but I'm not sure.
Hope that helps.
Sounds like an option however there is another consideration. What about apps that I have bought for my iphone? If I create a new itunes account and have itunes logged into that new id with match subscribed what will happen to my apps that were purchased under the old id? I would assume that I would only get updates etc and syncing of those if I was logged into the @me account rather than the new id which is not good either.
An iTunes library can be authorised for more than one account, so in theory it won't cause too much trouble for your Apps.
However, I used to have two accounts on my iTunes. Your assumption is correct in that Apps will only update if you are signed in on that ID. I had to keep on remembering to sign in on the other account for them to all update, which became a pain to do. In the end I spent about £15 repurchasing Apps so I could scrap the other ID.
I don't know what the consequence would be of signing in on the non match ID (i.e. whether it would switch Match off). I'd hope not, but I can't say for sure. Maybe someone else can help.