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Q in Q MTU advice

Hi i have a big customer who has a lot of switches and does trasport services between customers inside a location and multiple ISP.
Everything works well this far , i have configured vlans, trunking and allowing only the interesting traffic to pass between.
The problem is that today one ISP reqested a Q in Q L2 tunnel. I have made the configuration and i got this error.

%DOT1Q_TUNNELLING-4-MTU_WARNING:

System MTU of 1500 might be insufficient for 802.1Q tunnelling.

802.1Q tunnelling requires system MTU size of 1504 to handle maximum size ethernet frames.
Ok , i got it so far . I have to change the MTU and it requires me to reload the switch. (i cannot do this right now)

The problem is that i`m afraid that changing the MTU would create problems in the network so i kindly ask for your advice.
Changing the MTU is going to make my boss fire me because of the problems that will create ?
I have to mention that all the transport is done using 3750 switches ..but i don`t know what gear the customers have , i`m the Level 3 guy and i`m not in the site. Thanks a lot.

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