If you can't comply with the SID then you should tell us, if you're a 3 engine ferry, then you should tell us. We may have traffic to depart behind you that will quickly catch you up and then we have all the paperwork to do because you got too close to each other.
I would hope that a 4 engine a/c running on 3 engines woudn't have performance problems to such a degree as to not be able to comply with SID alt restrictions.