The JForex API exists to provide the functions you're looking for. An interactive strategy can achieve partial closes of a given position to any level of resolution (1 micro lot or greater per close increment).
I do it frequently from my own strategies.
As for asking for position splitting, it's best if you open positions individually and at different prices, so you don't have the need to split them later. Position merging is also something I do all the time, and you won't find that functionality at many brokerages other than Dukascopy, I'm pretty sure.
But partial closing achieves at least part of the goals which your proposed splitting appears aimed at providing anyway. I actually use this fine grained control, but do you really have a plan to use such functionality, even if it were ready made for you?
Highly customized Order Entry operations is why the programmable Strategy API mechanisms exist, but you're not likely to get highly specialized functions like that in the generic JForex platform.
Pay a competent programmer to give you the Strategy control you need. Then you'll get exactly what you want, but I'll bet you don't want to pay for it ?
My motto: Free software is worth every penny you paid for it !

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