Never have seen a written rule against this, whether BCA or whatever. Until someone produces such, I think it is moot, i.e., legal.
All the best,
WW
It is addressed in CSI BCAPL rules as follows:
1-2 Acceptance of Provided Equipment
1. Once your match begins, you accept all provided equipment as standard and legal. After a match has begun, only a referee or event official may declare the equipment defective or unsuitable for play. If the equipment is declared unsuitable for play, all games previously played on that equipment will be counted. (AR p. 78)
2. During a match, it is a foul if you attempt to modify provided equipment without the permission of a referee or event official. The foul occurs immediately upon the attempt, regardless of whether a stroke or shot is attempted. (AR p. 78)
1-2 Acceptance of Provided Equipment
In the event of sub-standard equipment, play might not be stopped or delayed unless conditions are severe. Particularly in tournament play, or other circumstances when time is limited, a match may be required to begin or continue on equipment such as a dirty or unlevel table. The final decision whether to start or continue play is solely at the judgment of the referee or Administrative Authority. If play continues, the Administrative Authority should make their best effort to correct the problem as soon as possible.
1. Situation: Player A, preparing to shoot a ball along the cushions and across the mouth of a side pocket, either pushes on the tip of the cushion or manipulates the cloth at the tip of the cushion at the side pocket.
Ruling: Foul, regardless of whether or not Player A attempts a shot.
AR are applied rules or examples and it is listed as a foul.