If you need to calculate only selected items in a Live Price Grid, you can trigger the partial calculation directly from a calculation flow:
actionBuilder.addLivePriceGridAction(label)
.restrictToSkus( [sku1, sku2, sku3] )
.setCalculate(true)
In the restrictToSkus method you need to specify the list of SKUs you want to recalculate. The behavior of the recalculation is the same as in the user action "'calculate" on a single Live Price Grid item.