Making speakers sound tonally similar with an equalizer

If you are asking the question of high fidelity consumer equipment… no. Equalization always has negative impacts on sound… so while you might make a few gross changes… you are going to lose fidelity by putting a bunch of pots or digitally manipulating the signal. For high fidelity the only serious game in town is get the signal right, pass it as transparently as possible through the amplification chain to the transducers.
 

In a high end research and development facility with many many hundreds of thousands of dollars worth of equipment,  sure. 

Make no mistake about it, the fun you can have with a $300 Schitt Lokius slightly modifying/shaping the sound of your speakers a no brainer.  No, of course it won’t change the sound of one speaker to sound like another.

While I say EQ's are a bad way to try to make one speaker sound like another, I've also seen Stereophile adopt B&W speakers as their reference, and Golden Ear matched it and got rave reviews... so... maybe there's something to it.

I’ve owned many speakers and they all sound different. I would say very difficult or impossible. Maybe if the speakers are in the same line- cabinet materials, driver materials, crossover components, etc. otherwise too many variables. I suppose frequency is frequency so there is an argument for it, but I say no way.

You might have better luck with a Realiser A16 and headphones trying to replicate certain speakers.