Record clamp/weight and turntable speed

I wouldn't worry one second about the slightly off-center weight, but if the aftermarket mat is thicker than the original, and if you have set VTA while using the OEM mat, then the VTA will have been altered by a tiny amount.  It's up to you to decide if that has affected SQ or tonal balance.  Probably not, is my guess.  If you are using a cartridge with a line contour stylus, which is very sensitive to VTA, listen carefully.

Mijo, I am getting a little excited about the idea of a "pulsating" anything, anywhere in my vicinity, given the dearth of human to human contact that characterizes my day to day existence during the pandemic.  Anyway, I have to disagree with my DD co-conspirator, Chakster, on at least one issue.  I do think that each type of drive system has its own sonic signature.  Guess which drive system I prefer.  I also think you ought to see someone about your fear of pulsating magnetic fields.  You are surrounded by magnetic fields, unless you live in a cave.  But seriously folks, I bought an EMI meter just to satisfy my curiosity about EMI in the vicinity of the cartridge that might be generated by the motor of a DD turntable.  Detected nothing at the platter surface.  This was with a Technics SP10 Mk3 which sports the largest iron-core motor of any vintage DD and probably at least as large as that of any modern DD.  I also checked my Kenwood L07D, which uses a coreless motor.  Nada.  Of course this observation is subject to the sensitivity of my meter. The fact that you personally may fear the negative effect of a DD motor on cartridge performance is not per se proof that there is any appreciable effect in reality.  The engineers that designed DD turntables in the first place were not unaware of the potential problem and were aware of how to use shielding and motor orientation in order to eliminate the problem. They did a good job.  Now, can there be a cheap, poorly designed DD turntable that adds its own noise to the audio signal?  Maybe.  Can there also be a cheap poorly designed BD turntable that is wildly inaccurate speed-wise?  Absolutely yes.

You provide no actual information.  How heavy is your record weight? What type of turntable do you use, belt-, idler- or direct-drive? Does the motor incorporate a speed control? What type? Have you actually measured speed with vs without the weight?  If not, how do you know that the speed is not affected at a level you cannot detect simply by listening for pitch, which is what I presume you do?  If you are concerned about your own record weight, you might consider switching to a record clamp, like the SOTA.  A clamp applies pressure to the LP against the platter mat surface but adds very minimally to the weight supported by the bearing.  Some don't like clamps because there is the potential to transmit noise from the bearing into the LP surface.