How do reserves and substitutes work in team events?

Bowls South Africa's domestic regulation on law 32.9 allows reserves and substitutes in all formats except singles:

• Reserve: a bona fide member of the same club (or district, in district events) registered with the team before the tournament starts. In triples and fours, one reserve may be registered and used.
• Substitute: used only if there is no reserve or the reserve is already playing. The names of up to four bowlers who have not played for any team in the tournament go into a hat, and the opposing coach (or captain) draws one. The substitute may play as many matches as needed but may not skip.
• Pairs: one of the original players must always be on the green. If the pair is already using a reserve or substitute and the remaining original player can't continue, the game is conceded. Mixed events may register two reserves, one of each gender.

Using a reserve or substitute this way does not count as fielding an ineligible player.