+1 Zio, this gives us the freedom to decide on the amount by the price of the balls.
As to the OP, this
Leiferiksen:When last ball of a kind is taken out of play during round it is automatically replaced by starter balls (no other options available)
describes the situation perfectly: Thou shalt not have any options available! Law 1 of WGT has been weakened by the "Mulligan" option of late, but only in practice play.
"No options!" stands strong in regular play!