This option is a bit hard to understand.
What is your primary concern? Do you want to load a file without calculating formulas, for example because the formulas already have been calculated by the source application? And later you want to have AutoCalc active, but you don't want to calculate the formulas again when AutoCalc becomes true.
Is your workbook loaded with so many formulas that recalculation takes a noticeable time? In this case you should consider to use another library because fpspreadsheet is not optimized for calcuilation speed.
Would it be ok to have an option boCalcAfterLoading which is on by default, but you could turn it off? Since AutoCalc is on by default you would not have to turn it on again and thus avoid the recalculation. boCalcAfterLoading would be a natural extension of the current workbook options where a boCalcBeforeSaving already exists.