iliyaz3,
Translating your aim to simplest words is: making a short-radius elbow dimensions out of a long-radius elbow.
According to ASME B31.3 the elbow becomes Unlisted Component, thus, it may be used but the limitations and requirements of 302.2.3 + 304.7.2 shall be met.
Please note that if your elbow's angle will remain of 90° - the new ends section you going to get will not be round, since B16.9 elbow does not have ends straight sections of 30mm as it seems from your sketch.
The only operation permitted by ASME B31.3 for ASME B16.9 fitting is angular adjustment of joint offset as follows:
328.4.2 (b)(6): "Buttweld fittings manufactured in accordance with ASME B16.9 may be trimmed to produce an angular joint offset in their connections to pipe or to other buttweld fittings without being subject to design qualifications in accordance with para. 304.7.2 provided the total angular offset produced between the two jointed parts does not exceed 3 deg".