Yes, that one change (well, two components) can often be enough, as it has a four-fold benefit-Reduce value of the grid feed bias resistors (typically 220K)
The gain and output voltage swing of the LTP is reduced a little, increasing the margin of stability and reducing bias excursion under overdrive.
The time constant at the power tube control grids (formed by the coupling cap and grid leak resistance) is lowered, further reducing bias excursion under overdrive, see http://www.ampbooks.com/mobile/amplifie ... excursion/
Lower grid leak resistance results in a more stable amp, more able to accommodate higher levels of control grid positive current; note that the limiting value for control grid resistance of 6L6~ in fixed bias is 100k.