you don't need to gradually switch them over, just switch them over. It might take a a day or 3 for them to eat it well this happens with any diet change sometimes.
No, there are no other fruits and veg you can feed with it. Yes, it seems limited. But the fruits and veg have been nutritionally calculated in to the entire diet plan. If you feed other fruits n veg it makes the diet unbalanced. It may be "limited" but that is not necessarily a bad thing. Consistency vs variety. The "limited" fruits and veg make this diet the most consistent one in my opinion. There are still ways to offer variety, using the same fruit and veg. It's all in how you serve it.
Example
mon bml, corn, cherries
tue bml, peas, grapes
wed bml, beans watermelon
thurs bml, carrots, apples
fri bml, mixed veg, honeydew
sat bml, peas and carrots, blueberries (blueberries are on the bml list)
sun bml, beans, grapes
this is a simple example of how you can use the fruits n veg and still offer variety
while still keeping the diet consistent.
yes kiwi are safe, none of mine like it though