Modx needs a Pattern lock that locks recording patterns when jumping to category to find the next instrument.

May we suggest you recognize the following navigation tip;

Once you have selected your Performance and enter the Pattern Sequencer, you can work within just that Performance by recognizing the following:

Touching “Play/Rec“ or pressing the [PLAY] button will always allow you to continue work on the current Pattern and Performance. So say you stopped the Sequencer and want to go into the Performance to Edit some deeper level parameters or make controller assignments, fine do so, but when you are ready to return to working on your current Pattern, do so by either touching “Play/Rec” in the first column of the screen or simply pressing the [PLAY] button. (In other words, do anything EXCEPT press [RECORD]).

If you press the [RECORD] button, the Sequencer will increment to a NEW blank Pattern.
It’s a feature! Not something that needs correcting, only your knowledge of the meaning of pressing RECORD when not in the Sequencer proper. You’ll find yourself using this (now that you know about it) when you actually do want to create a NEW sequence!

When not in the Pattern Sequencer, if you press Record, it assumes you are ready to make a NEW Sequence.

Tapping “Play/Rec” in the first column of the screen returns you to your current or most recently selected Pattern.

Once you know to do this, you stop thinking you need a “Pattern lock”... you simply need to stop pressing the RECORD button when not actually ready to Record (Ready to Record means you are already looking at the Pattern screen, looking at the Measure counter, setting Length, etc).

Additionally, we should mention, when adding “+” new Parts to your Performance Pattern, it is not necessary to leave the Pattern area, you can interact with Part Selection by directly tapping the Part slot to activate the search. You can return to your Pattern screen by pressing [EXIT]

Also need a pattern randomizer, a randomize chords and a random drum break.

I’m afraid you’d need to define what those are... as you know there are initially no Patterns to randomize, there are no chords to randomize, and there are initially no drum breaks to randomize.

If you are referring to the Arpeggio Phrases, among the 10,231 Phrases you will find all manner of Phrases and types. Much can be done to expand on this provided content by applying the real-time Arp Offsets (before recording) Swing Quantize, Gate Time, Velocity Offsets, etc. And after you have recorded the Arp’s to the Sequencer applying the Play FX on recorded Pattern data can intelligently alter the data. Please see the features added in the recent updates (2.0 and 2.5) concerning Play FX 1 and 2.

Extra Credit:
When connected to Cubase, you can create a CHORD Track. Any of the Parts can be set to follow the Chord Track entries — this can immediately reharmonize the recorded data.

https://youtu.be/c_YR3WduUNY

You may also want to look into Groove Agent as a resource for Drum Breaks and randomizing complexity of drum data