I assuming with the reindex that you're currently doing, you have turned the pruning off? If so, you can switch the wallets whenever you like, with a quick rescan of course. You can just replace the wallet.dat in the data directory, or if you have several you can just put all of them in the data directory and naming each of them differently (wallet1.dat, wallet2.dat, etc). You can open them by clicking on the file at the top left and go to Open Wallet in Bitcoin Core. You should be able to switch the wallet.dat as and when you like.
Bitcoin Core should automatically do a rescan and that can take several minutes to an hour. It should show rescanning... with the start up screen.
Thank you for taking the time and sharing your knowledge. This is very useful. I didn't know that multiple wallets can be placed in the wallet directory. And, yes, when I started the loading the entire blockchain again, I noticed the option to turn off the pruning mode. Only then did I understand how I got in this situation in the first place. I've only got 50 Aus dollars in the wallet but the whole exercise is to be confident in buying and storing an investment. Thanks so much for helping out.