How do I create guides within shapes?

One could use locked Shape Layers as a substitute.

Unfortunately this method extends the guides outside of the shape and into other shapes, which clutters everything else and makes it all confusing.

I already mentioned in post 1 that this behaviour of guides is not avoidable in Photoshop (as of now).

Try this script. You can change the number of divisions in line 2.

#target photoshop
var num = 6
var doc = activeDocument;
var lay = doc.activeLayer
var horSize = parseFloat(lay.bounds[2]-lay.bounds[0]);
var vertSize = parseFloat(lay.bounds[3]-lay.bounds[1]);
var horSpace = horSize/num;
var vertSpace = vertSize/num;
var hStart = parseFloat(lay.bounds[0]);
var vStart = parseFloat(lay.bounds[1]);
for(var i=0;i<num +1;i++){
    mGuide ('h', hStart + horSpace*i)
    mGuide ('v', vStart + vertSpace*i)
    }
function mGuide(orient, loc){
    var idMk = charIDToTypeID( "Mk  " );
        var desc12 = new ActionDescriptor();
        var idNw = charIDToTypeID( "Nw  " );
            var desc13 = new ActionDescriptor();
            var idPstn = charIDToTypeID( "Pstn" );
            var idPxl = charIDToTypeID( "#Pxl" );
            desc13.putUnitDouble( idPstn, idPxl, loc );
            var idOrnt = charIDToTypeID( "Ornt" );
            var idOrnt = charIDToTypeID( "Ornt" );
            if(orient =='v'){
                var idHrzn = charIDToTypeID( "Hrzn" );
                }
            else{
                var idHrzn = charIDToTypeID( "Vrtc" );
                }
            desc13.putEnumerated( idOrnt, idOrnt, idHrzn );
            var idKnd = charIDToTypeID( "Knd " );
            var idKnd = charIDToTypeID( "Knd " );
            var idDcmn = charIDToTypeID( "Dcmn" );
            desc13.putEnumerated( idKnd, idKnd, idDcmn );
            var idnull = charIDToTypeID( "null" );
                var ref3 = new ActionReference();
                var idDcmn = charIDToTypeID( "Dcmn" );
                ref3.putIdentifier( idDcmn, 197 );
                var idGd = charIDToTypeID( "Gd  " );
                ref3.putIndex( idGd, 2 );
            desc13.putReference( idnull, ref3 );
        var idGd = charIDToTypeID( "Gd  " );
        desc12.putObject( idNw, idGd, desc13 );
        var idnull = charIDToTypeID( "null" );
            var ref4 = new ActionReference();
            var idGd = charIDToTypeID( "Gd  " );
            ref4.putClass( idGd );
        desc12.putReference( idnull, ref4 );
        var idguideTarget = stringIDToTypeID( "guideTarget" );
        var idguideTarget = stringIDToTypeID( "guideTarget" );
        var idguideTargetCanvas = stringIDToTypeID( "guideTargetCanvas" );
        desc12.putEnumerated( idguideTarget, idguideTarget, idguideTargetCanvas );
    executeAction( idMk, desc12, DialogModes.NO );    
    }

Good day!

Photoshop guides are not terribly advanced, they currently always extend over the whole width or height (depending on their orientation).

But maybe I misunderstood your point, could you post a screenshot or mock-up to clarify?

Regards,

Pfaffenbichler