That is correct but only if you use BertForSequenceClassification.from_pretrained to load the existing weights. You can then use that model to further train the model. If you do not use from_pretrained, you will train a new model from-scratch and that is probably not what you want.
This process is called finetuning the model on a downstream task. Do not call it pretrain, that is confusing. Pretraining is the initial training that was done to get the weights that currently exist in the models that we can use.