How can I add a new layer fc8 instead of deleting last layer ?

(roi_heads): RoIHeads(
(box_roi_pool): MultiScaleRoIAlign()
(box_head): TwoMLPHead(
(fc6): Linear(in_features=12544, out_features=1024, bias=True)
(fc7): Linear(in_features=1024, out_features=1024, bias=True)
(fc8): Linear(in_features=1024, out_features=1024, bias=True)
)
(box_predictor): FastRCNNPredictor(
(cls_score): Linear(in_features=1024, out_features=91, bias=True)
(bbox_pred): Linear(in_features=1024, out_features=364, bias=True)
)
)