I'll assume a single LiIon or LiPo battery - nominally 3.6V, actually <= 4.2V and as low as about 3V. Some devices MAY use eg 2 cells and 7.2V and use a boost converter for charging, but this is rare.
If you are willing to access the tablet battery connections and to possibly use an external charger or even an external battery or power supply then you will be able to run it as 100% brightness continually, subject to cooling issues. See "The easy way" below.
If not, then:
There are two most likely internal circuit arrangements.
Also some variants, but the following two should cover most cases.
In one case - power input goes to device always and only via the battery, a higher current power supply will not help. This is because the internal charger is limited to 2A and the path to the device is via the battery so 2A is your limit.
In the other case - power supply goes to device proper and battery is charged from this point, a higher current supply may help. This is because the battery is "backfed at 2A max by the supply but there is also a direct path from external supply to device.
In ether case it is probable that NO damage will be caused by a higher current supply - but this is not 100% certain.
The easy way
If you can disconnect the battery and feed the battery terminals with a 'virtual battery' with enough current capability then you should be able to operate the device continually at 100% brightness. Say for discussion that Imax is 3A. If you connect a power supply capable of providing >= 3A at anywhere from about 3.2V to 4.0 V to the battery terminals (~ 3.6V best voltage if selectable) then the device will see this as a battery and operate correctly. The supply should be able to provide any startup or other transient peaks (if any) and MUST NEVER provide voltages outside the usual battery range.
The external supply could be a battery plus a charger capable of sourcing >= 3A.
As long as you do not connect power to the device charging input it will see the externally connected power source as a discharging battery.