I read that one of the British Governors of British South Africa want to have the British Veterans of the Crimean War migrate to South Africa. It was my understanding that they would be give small land grants and become farmers.
They were, to an extent. The men of the
British German Legion, which was just about ready to go to the Crimea when Sebastopol fell, were offered land in South Africa in return for acting as an auxiliary military force there. Some later rejoined the army to serve in the Indian rebellion: ten years later, some were part of the expedition to Abyssinia.
The problem with the suggestion is that, although some of these temporary organisations got disbanded, the British regular army didn't really demobilise after the Crimea. They went up from c.150,000 in 1853 to c.220,000 in 1856, down to c.196,000 in 1858, and then back up to c.222,000 in 1861. The wider changes probably butterfly a lot of developments- for instance, if you don't have an Indian rebellion, you probably end up with a dramatically different attitude towards colonies and imperialism in Britain.
The other thing to bear in mind is capacity. If you can find 20,000 veterans to discharge in 1858, they probably edge out other British settlers who would have gone to South Africa, but now end up in Canada or Australia or New Zealand instead.
The white populations (British and Afrikaner) for all four South African states in 1904 (i.e., after Boer War losses) are:
Cape Colony: 579,741 (c.3:2 Afrikaner:British)
Natal: 97,109 (c.90% British)
Orange River Colony: 142,679 (perhaps 80% Afrikaner)
Transvaal: 297,277 (maybe 50:50)