An existing plant is going to be genetically programmed to produce a certain type, size and sweetness of berry. That being said, all plants will produce differently depending on conditions. So, good soil, good sun, good water. Keep competing plants and weeds away. If the plant produces a lot of fruit buds, remove up to half of them. Good polination also produces bigger berries. Still, wild blueberries will never produce fruit the size of varieties that have been selected for large fruit.

Pruning some berries off might...a little. The commercial varieties have been developed through selective breeding practices and hybridization. The smaller berried bushes typically don't have the genetic potential for big berries, but random exceptions do occur.
The wild blueberry harvesters of the north east, more than a century ago, began gathering specimens that they found during harvesting that they deemed superior for one or several reasons. Big berries and small seeds, flavor, productivity, bush size, disease resistance, etc.
These crosses yielded the earlier and now rarely grown varieties such as Pioneer, Pemberton, Rancocas, Rubel, etc.
These varieties were later crossed and selections were made to fit a developing industry with mechanization in mind.
Varieties like Jersey were selected through these crosses and later crossed with other previous, distinct combinations to produce sisters like bluecrop and blueray.

So a great deal of selective breeding to bring forth recessive expressions of genes like size, and blueness or bloom, take a lot of sorting and only once in a while appear in nature. And it was these exceptional wild varieties that came together to give us our big fat berries. Some wild ones taste awesome. Use them in your muffins and relish their compact goodness.
noogy