Good idea to swap McIntosh amp stock tubes?

No decently designed amplifier should suffer any adverse issues from replacing stock tubes with different brands as long as they are the same type of tube.  If you have a 12AX7 in a circuit, replace it with a 12AX7.  The amp will be in no danger of malfunction (unless the tube itself is defective). McIntosh should certainly qualify as a competently designed amp. 

Now, whether or not you like the sound quality better or not, or whether you have the same opinion as to whether the original tubes selected by McIntosh represent the best sound the amp can deliver, are wild cards. It's your amp so you're free to use the tubes you prefer. 

"Tube amplifiers that reflect sound changes when tube swapping occurs may not be designed very well. you shouldn't need to change out the tubes to improve sound of your amplifier."

Is this your contention or are you quoting McIntosh?

@emergingsoul 

Tubes last a long time in Mcintosh Tube amps and preamps.  Well matched great quality tubes will give you the best sound. 

I use two MC275s amps in monoblock mode and a McIntosh C2300 tube preamp  I put away the McIntosh tubes as spares a long time ago - 2013.  For the preamp, I use Telefunken smooth plate 12ax7 vintage tubes bought on ebay.  They sound great in the line stage and MC phone stage.  In the amps, for the power tubes, I prefer - New Matched Octet (8) Genalex Gold Lion KT88 Reissue Vacuum Tubes (note: VIVA tubes usually has a good price),  and learned on this forum -   the frame grid JJ E83CC - 12AX7 (tube depot carries them).  For 12AT7, pick your poison, but, I use NOS MATCH QUAD *D* GETTERS 5 STAR 6201 ECC81 12AT7 3 MICA TUBES USA MADE 1950’S (ebay has cheap prices on these).   All of the tubes I mention are still relatively inexpensive and perform extremely well in my Mcintosh amps.  Yes, the small tubes will wear out before the big power tubes.  12AT7 first, then, 12AX7, then, the KT88 power tubes.  In the Mc275s, this is the order of highest to lowest wear over time.   Note: You can see my stereo rig in my signature,. 

Note:  Regarding sound influence from most to least, my opinion is the Pre-amp Tubes first - 12ax7, Amp small tubes 12ax7 second, Amp small tubes 12at7 third, and the Power Tubes KT88 last. 

My experience differs from hjdca.  In my MC2000 the original tubes lasted 10 years before one of the power tubes went.  At that time I replaced the complete tube set.  I bought Gold Lions for the power tube replacements, and my tube guru chose replacements for me for the small tubes.  After 7 years one of the Gold Lions went and I bought another set of the same.  I use the amp less frequently these days and haven't had any issues since.  But my experience and belief is that the power tubes do not last as long as the small tubes.  By quite a bit, actually.

Bill

What you need to take into account is that most top end manufacturers using tubes burn their tubes in and then test them thoroughly to select the parameters that are optimal in the intended place in the circuit.

So for example, they may use the same tube in their preamp and power amp, but you will find that they have selected tubes with specific performance parameters for phono or line etc, even down to what type of circuit the tube is used in.

In other words, quality manufacturers will buy in the tubes, run a burn in and selection process and then sell off what is outside the parameters required to tube resellers.

When you buy the same tubes from a reseller, chances are despite being carefully matched, it has probably already been rejected by a manufacturer, not because it is poor, but because certain parameters are outside the requirements they are looking for.

When you buy expensive NOS tubes, they can be an improvement, but the downsides are that if they are not optimum you might well find they are noisy ( most modern tube gear run tubes very hard to get linearity ) or not last - and if 1 goes you have to find another pair. If I use NOS I go for a matched quad for a single pair of tubes.