If I understand you correctly (I don't fly the 777); After you have entered route + ZFW + CRZ alt, the box will have the means to calculate your T/C and T/D. If you have a constraint before your T/C, then naturally this will be a constraint in the VNAV climb path. If for some reason you have a constraint in the CRZ path lower than entered CRZ alt, you'll get the message unable CRZ alt. And finally, any constraints after T/D will be for your VNAV descent path.