If the original sponsoring employer applied under cap-subject/lottery and you never worked for the sponsoring employer or activated your H1B by visa stamping, USCIS may not approve another employer sponsoring your H1B under cap-exempt. Technically it is not a change of employer petition aka transfer as that can only be filed if you are working for a H1B sponsoring employer in the US.
That said, there have been instances where USCIS has approved cap-exempt H1B even if the beneficiary never worked for the sponsoring employer.
My suggestion would be to at least go for visa stamping using the H1B approval notice from the original sponsoring employer and then have your current employer file for new cap-exempt H1B petition under premium processing. Meanwhile your H1B from current employer is processed, buy time from your original sponsoring employer so their door is open if H1B petition from your current employer is denied for whatever reason. If it is approved and you decide to work for your current employer, you can use the visa stamp to travel to the US and start working for your current employer. Otherwise you can join your original sponsoring employer.