Smudge tool "finger painting" option shortcut

Did my reply from Photoshop Event Manager: Listen for key pressed to execute script solve your problem?

script toggles "finger painting" state

#target photoshop;

var s2t = stringIDToTypeID,
    t2s = typeIDToStringID,
    c2t = charIDToTypeID;

(r = new ActionReference()).putProperty(s2t('property'), p = s2t('tool'));
r.putEnumerated(s2t('application'), s2t('ordinal'), s2t('targetEnum'));
var tool = executeActionGet(r);
var t = t2s(tool.getEnumerationType(s2t('tool')));
if (t == 'smudgeTool') {
    (d = new ActionDescriptor()).putBoolean(c2t('SmdF'), !tool.getObjectValue(s2t('currentToolOptions')).getBoolean(c2t('SmdF')));
    d.putBoolean(s2t('useScatter'), tool.getObjectValue(s2t('currentToolOptions')).getBoolean(s2t('useScatter')));
        (r = new ActionReference()).putClass(s2t(t));
    (d1 = new ActionDescriptor()).putReference(s2t('target'), r);
    d1.putObject(s2t('to'), s2t('target'), d);
    executeAction(s2t('set'), d1, DialogModes.NO);
}

You can press Alt or Option while using the Smudge Tool to toggle Finger Painting.

(you won't see the Finger Painting box get checked/unchecked when using Alt/Option)

That is, if you want to switch to Finger Painting, press and hold the Alt/Option key then starting painting.

It will not toggle between the two while actually painting with the Smudge Tool.

 You can tell if your Finger Painting if the beginning of the stroke starts with the color that is set in the Foreground color chip in the tools panel.